)/o FaFt^.— No, I. 



aoy^ 




iGRICULTURAL CHEMISTEY, 



FOa THE USE OF 

A€il)E»liES, SCHOOLS, AND AGRICULTURALISTS: 

coMPRisma 

rJL\T PORTLON OF ELEMENTARY CHEMISTRY WHICH IS NECES- 
SAKY TO A FULL UNDERSTANDING OF THE CHANGES CON- 
NECTED WITH VEGETABLE ORGANIZATION, 

AND 

AN EXAMINATION OP THE DIFFERENT MANURES, 
SOILS, CROPS, &c., COMPILED IN PART FROM 
THE WRITINGS OF PETZHOLDT, JOHNS- 
TON, LIEBIG, AND OTHERS. 



By ASAHEL K. EATON, M. A., 

PROFE-SSOR 6F THE NATURAL SCIENCES IN LITTLE FALLS ACADEMY. 

UTICA: 
H. H. HAWLEY & CO., and G. TRACY. 

18 4 7., 




Price Tweiitj^-live €eets, 




Copyright }^". 



COPYRIGHT DEPOSIT. 



Digitized by the Internet Archive 
in 2010 with funding from 
The Library of Congress 



http://www.archive.org/details/textbookonagricuOOeato 



1 



_J -^r. k>^^ ''^ y 



TEXT-BOOK 



AGRICULTURAL CHEMISTRY, 



FOR THE USE OF 

ACADEMIES, SCHOOLS, AND AGRICULTURALISTS; 

COMPRISING 

THAT PORTION OF ELEMENTARY CHEMISTRY WHICH IS NECES 
SARY TO A FULL UNDERSTANDING OF THE CHANGES CON- 
NECTED WITH VEGETABLE ORGANIZATION, 

AND 

AN EXAMINATION OF THE DIFFERENT MANURES, 
SOILS, CROPS, &c., COMPILED IN PART FROM 
THE WRITINGS OF PETZHOLDT, JOHNS- 
TON, LIEBIG, AND OTHERS. 



iiJ 



By ASAHEL K. EATON, M. A., 

PROFESSOR OF THE NATURAL SCIENCES IN LITTLE FALLS ACADEMY. 

UTICA: 
H. H. HAWLEY & CO., and G. TRACY, 

1847. 



Entered according to Act of Congress, 

By Asahel K. Eaton, 

In the Clerk's Office of the Northern District of New York, 

in the year 1847. 



D. BENNETT, Pkintek, 
156 Genesee St., Utica. 






s 



I 



TO 



^ DANIEL WASHBURN, ESQ., M. A., 

^ FBINCIPAL OF LITTLE FALLS ACADEMY, 

-K" ®l)i5 tlolumc 

IS RESPECTFULLY DEDICATED 

THE AUTHOR, 

AS A TRIBUTE OF ESTEEM FOE ONE WHO EVER MANIFESTS 
A DEEP INTEREST IN THE ADVANCEMENT OF SCI- 
ENCE, AND ESPECIALLY IN THE SUCCESSFUL 
APPLICATION OF ITS PRINCIPLES TO 
THE USEFUL ARTS 




PREFACE. 



The demand for a text-book on Agricultural Chemistry, embracing 
that part only of chemical science which is intimately connected with the 
process of vegetable organization, has long been urgent. 'I he publica- 
tion of this volume is intended to supply that demand, and if it should 
prove the means of awakening a still greater interest in the beautiful 
changes connected with the phenomena of vegetable life, and of aiding 
the practical farmer in his endeavor to make fruitful the barren earth, the 
author will feel sufficiently rewarded. 

There is a prejudice existing in the minds of some against " book farm- 
ing" as it is called ; the cause of this prejudice has been pointed out in 
almost the last words of a departed statesman, who was endeared to many, 
respected by all. " In many cases visionary experiments have been in- 
troduced, based upon no philosophical investigation of cause and effect, 
but upon some accidental trial by a single individual, of some novel mode 
of culture, which, under the circumstances attending the experiment has 
met with success. This single experiment, without an inquiry into, or 
knowledge of the cause, which, in the given cases has secured the suc- 
cessful results, is at once recommended as an infallible rule of husbandry. 
The publication and dissemination of detached experiments of this char- 
acter, for a long period constituted the most material additions to the 
stock of literary information, connected with agriculture, supplied to 
our farmers ; while many of the experiments were too intricate and com- 
plicated to be reduced to practice with any certainty of accuracy, and 
others were so expensive that the most perfect success would not warrant 
the outlay. Unsuccessful attempts to fuUow the directions given for 
making these, brought what came to be denominated "book farming" 
into great disrepute with the industrious, frugal and successful farmers of 
the country, and excited a jealousy of, and a prejudice against this de- 



6 PREFACE. 

scription of information upon agricultural subjects, which it has caused 
years of patient and unceasing effort in any measure to allay, and which 
are not yet removed." 

The deductions of chemical science are not theories; they are well 
defined and immutable laws ; laws which never can be varied, for they 
were established at the dawn of time by the highest power, for the gov- 
ernment of matter. The chemist sees changes occurring in the vegetable, 
animal, and mineral kingdoms, and it is his great inquiry, " What is the 
cause of this or that phenomenon I" In settling this question he has re- 
course frequently to theories ; by experiments he tests the validity of 
these ; if the true cause be once determined, he does not hesitate to as- 
sert that the same cause will ever produce a similar effect, in short he 
thus establishes the existence of a law. 

It is true that there are very many points as yet unsettled in science, 
and many theories have been advanced to account for the phenomena 
connected with them ; but it is easy to distinguish between the unfailing 
deductions of science and the uncertain assertions of theory. If a crop 
flourishes vigorously upon one soil, but upon another either fails entirely 
or is of a sickly growth ; it is not impossible to ascertain the cause of the 
difference in agricultural capacity of the two soils ; and knowing the ele- 
ments that are wanting in that which is sterile, by proper treatment we 
may render it equal in productiveness to that which is naturally more 
fruitful. Some study is required in order to gain the requisite knowl- 
edge of the chemical constitution of plants, soils, and manures, but 
there is a manifest unwillingness, on the part of the practical farmer, to 
bend the mind to the acquisition of that elementary knov,'ledge which is 
absoluttly essential to the full understanding of whatever is written upon 
agricultural science. 

Practical agriculturalists complain, and not without reason, that those 
works which treat of this department of science, although written by the 
ablest chemists, are of no use to those who ought to be most benefited by 
them, because their works are so interspersed with technical terms and 
hard names that it is impossible for those who are not chemists to un- 
derstand them. The fault is to be attributed in part to the writers, in 
part, to the readers, of these treatises. On the one hand, such men as 
Lieb^g, Johnsion, &c., have become so familiar with the use of chemical 
terms, that they do not consider that most men know very little of them, 




PREFACE. 7 

and hence they make use of such terms, even when common names might 
be substituted. On the other hand, many individuals have neglected to 
gain a knowledge of the elementary principles of chemistry, and there- 
fore can not understand a general treatise upon the application of this 
science to agriculture, even if it is written in the simplest style possible^ 
for, to many of the elements and compounds concerned in vegetation, no 
common names are given, and therefore chemical terms must be applied. 

The superiority of chemical names over these in common use, is not 
justly appreciated ; the latter usually mean nothing ; the former gener- 
ally indicate the exact constitution of the substances designated or their 
peculiar properties. In the following pages, the common name is used 
whenever any such exists, and the chemical term is given in connection 
with it. Rules also are given which enable the learner by a very little 
study, to determine the constitution of a compound from its name, or its 
name from its constitution. 

It has been the endeavor of the author to introduce only that portion 
of elementary chemistry which is essential to a full understanding of the 
changes occurring in the vegetable world ; in the last part of the work 
the principles of the science are applied, and the nature and action of 
different manures, the capabilities of different soils, and the kind of food 
demanded by different plants, successively examined. 

Acknowledgements are due to the various authors quoted in the course 
of the work ; no apology to the reader is required for compiling from the 
writings of such chemists as Johnston, Petzholdt, Draper and Liebig. 

Little Falls, Dec. 1847. 



AGRICULTURAL CHEMISTRY. 



PART L 

ELEMENTS. 



SECTION 1. 

CONSTITUTION OF MATTER. 

Notwithstanding the variety o^ forms which the 
matter constituting the world assumes, there are, in 
reality, only about fifty-eight different simple substan- 
ces, and the combination of these has produced most of 
the objects which we see around us. These simple 
substances are called elements. Gold, silver, copper, 
mercury, iron, sulphur, &c., are elementary substances, 
whilst air, water, earth and most kinds of matter with 
which we are familiar, are compound, formed by the 
combination of different elements. 

There is a mineral — iron pyrites — that very nearly 
resembles gold, but, by subjecting it to certain tests, it 
is resolved into two substances, iron and sulphur. It 
is not then an element, because, by decomposition we 
obtain from it two different elementary substances : but 
goldy though very similar to this mineral in appearance,^ 
is an element, because it has never been decomposed. 

How many different simple substances are there 1 How are most of the 
objectswhich we see around us, produced 1 What name is given to these 
simple substances 1 Mention some elements — some substances that are 
not elements. What is said of a certain mineral resembling gold T Is 
it an element 1 



14 AGRICULTURAL CHEMISTRY. 

Those bodies, whether solids, liquids or gases, which 
have never been decomposed, or divided so as to pro- 
duce two or more different substances are called ele- 
ments ; some of these, by farther investigation matf 
prove to be compound. 

The science of Chemistry owes its origin to the fact 
that the number of simple substances is limited. Did^ 
the earth consist of but one elementary substance — iron 
for example- — such a science would be uncalled for. If 
it were composed of as many as it seems to be to the 
uneducated, it would be almost impossible to establish 
such a science. 

It is the legitimate object of Chemistry to point out 
the elements of which matter is composed, the laws 
which govern the union or separation of those elements, 
and the properties of the compounds formed by their 
combination. 

By applying this science to the vegetable forms which 
flourish upon the earth, and to the manner in which they 
are nourished, we ascertain the elements of which plants 
are composed ; the constituents of the soil, and the sub- 
stances which it is necessary to supply to the soil, a& 
food for the plant. 

It is the province of Agricultural Chemistry then, to 
treat of those elements of which plants are composed^ 
and the manner in which they are obtained, retained 
and united, to form vegetable substances. 

In treating of the simple substances in this work, we 
shall dwell upon those only which are concerned in the 
formation of plants, since we do not wish to burden the 
mind with that which does not pertain to Agricultural 

What substances are called elements ? May some now called ele- 
ments, prove to be compound ? If the earth consisted of but one element, 
would there be any necessity for such a science as Chemistry 1 What 
would be the result if there were as many different simple substances' 
as there are different forms of matter % What is the object of chemistry % 
What is the province of agricultural chemistry % 



ELEMENTS. 



15 



Chemistry. A list is given, however, of all the elements 
known, with the abbreviation or symbol, which is gene- 
rally written instead of the whole name. 



Elements with their Symbols and Atomic Weights. 



Nou-metuUis i£lenienis. 

Oxygen 

Hydrogen 

Nitrogen 

Carbon 

Boron . 

Silicon . 

Sulphur 

Selenium 

Phosphorus 

Chlorine 

Iodine . 

Bromine 

Fluorine 

Metallic Elements. 

Potassium 

Sodium 

Lithium 

Barium 

Strontium 

Calcium 

Magnesium 

Aluminum 

Glucinum . 

Yttrium . 

Zirconium 

Thorium . 

Cerium 

Lanthanum 

Didymium 



Symbols. 


At. wts. 


0. 


8013 


H. 


1-000 


N. 


14-19 


C. 


604 


B. 


10-91 


Si. 


22 22 


S. 


1612 


Se. 


39-63 


P. 


15-72 


CI. 


35-47 


L 


126-57 


Br. 


78-39 


F. 


18-74 


K. 


39-26 


Na. 


23-21 


L. 


6-44 


Ba. 


68-66 


Sr. 


43-85 


Ca. 


20-52 


Mg. 


12-89 


Al. 


13 72 


G. 


26-54 


Y. 


3225 


Z. 


33-67 


Th. 


59-83 


Ce. 


4605 


La. 




D. 





Metallic £leiiaents, 

Erbium 

Terbium 

Manganese 

Iron 

Cobalt . 

Nickle . 

Zinc 

Cadmium 

Lead . 

Tin. . 

Bismuth 

Copper . 

Uranium 

Mercury 

Silver . 

Palladium 

Rhodium 

Iridium 

Platinum 

Gold . 

Osmium 

Titanium 

Tantalum 

Tellurium 

Tungsten 

Molybdenum 

Vanadium 

Chromium 

Antimony 

Arsenic 



Symbols. 

E. 

Tr. 

Mn. 

Fe. 

Co. 

Ni. 

Zn. 

Cd. 

Pb. 

Sn. 

Bi. 

Cu. 

U. 

Hg. 

Ag. 

Pd. 

R. 

Ir. 

Pt. 

Au. 

Os. 

Ti. 

Ta. 

Te. 

W. 

Mo. 

V. 

Or. 

Sb. 

As. 



22-72 

2800 

29-57 

29-62 

32-31 

55-83 

103-73 

58-92 

71-07 

31-71 

217-20 

202-87 

10831 

53-36 

52-20 

98-84 

98-84 

199-2 

99-72 

24-33 

184-90 

64-25 

99-70 

47-96 

68-66 

28-19 

64-62 

37-67 



It will be seen that these elements are divided into 
metallic and non-metallic, 13 of the latter, 45 of the 
former. The column of atomic weights gives the sup- 
posed comparative weight of an atom of each elemen- 
tary substance. It is supposed that there is a limit to 

For what are symbols used ? How are the elements divided ? What 
is indicated by the numbers in the column marked " atomic weights]" 



16 



AGRICULTURAL CHEMISTRY^ 



the divisibility of matter, and those exceedingly minute 
particles of which a substance is supposed lo be made 
up, are called atoms. The comparative weight ot an 
atom of zinc and one of sulphur, are as the numbers 
32 31, and 16-12, or, as they are generally given, 32 and 
3 6. This is inferred from the circumstance, that if we 
decompose the simplest combination of these elements, 
which is an ore called zinc hknde ; we shall obtain 32 
parts by weight of zinc, and 16 of sulphur from 48 
parts of the ore. 

The following list contains the names of those ele- 
ments only, which are concerned in the production of 
vegetable 'forms. The atomic weights are given ap- 
proxiraatelv. 

Elements which constitute Plants. 



Non-Metallic EUmeiits, 

Oxygen . . . 

Hydrogen . . . 

Nitrogen . . . 

Carbon , . . 

Silicon . , . . 

Sulphur . . . 

Phosphorus . . 

Chlorine . . . 

Iodine . . . , 

Bromine . . . 

Fluorine . . . 



Symbols. 


At.Wts. 


0. 


8 


H. 


1 


N. 


14 


C. 


6 


Si. 


22 


s. 


16 


p. 


16 


CI. 


36 


I. 


126 


Br. 


78 


F. 


18 



Metallic Elements. 


Symbols. 


Potassium . . . 


K. 


Sodium . . . 


Na. 


Calcium . . . 


Ca. 


Magnesium . . 


Mg. 


Iron .... 


Fe. 


Manganese . . 


Mn. 


Aluminum . . 


Al. 



At.Wti 

40 
24 
20 
12 

28 
28 
14 



These 18 elements are the only ones concerned in 
the process of vegetation, and of these, the first, second 
and fourth, form by far the larger proportion of the 
plant, — from 88 to 99 per cent. But notwithstanding 
the minute quantity of the other elements, a certain 
proportion, though very small is absolutely required : 
except a few of the elements which occur in certain 
plants only. 

What are atoms'? Why are 16 and 32 given as the atomic weights of 
sulphur a-nd zinc ] How many elements are concerned in vegetation ? 
Which of these constitute the greater share of the plant? What pro- 
portion 1 Are the other elements essential to the perfection of the plant i 



OXYGEN. 17 

it is of the first importance that the student should 
pursue this study systematically, and in order to do 
this, he should first obtain a knowledge of these elemen- 
tary substances, then of the compounds formed by the 
union of the same, and lastly, of those agencies by which 
the various changes are wrought, which are continually 
going on in the vegetable world. In this way he will 
obtain a knowledge of that part of elementary chemis- 
try which is directly applicable to agriculture. 



SECTION II. 

OXYGEN, HYDROGEN, NITROGEN, & CARBON. 

Oxygen. 0=8o 
Fig. L 




If we introduce a portion of red precipitate into a re- 
tort^ {a, Fig. 1,) and apply heat by means of a spirit 
lamp, a bright metal will soon begin to accumulate in 
the receiver (6) ; it is a liquid at ordinary tempera- 
tures, and is called Mer^mry. Whilst this metal is dis- 

What is the symbol for Oxygen 1 What its atomic weight ? What 
substance is placed in the retort, in the process represented by Fig, 1 ? 
What metal distills over and accumulates in the receiver ? 



18 AGRICULTURAL CHEMISTRY. 

tilling over from the retort, bubbles will appear at the 
end of the tube (c) which passes into the water of the 
cistern. The tall glass jar is filled with water, and in- 
verted with its mouth over the end of the conducting 
tube ; as the bubbles of gas pass from the tube, they 
rise in the jar and displace the water. 

This gas is called Oxygen, and is the first in the list 
of elements. 

It will be seen at once that it is very similar to air in 
its physical properties, being transparent, colorless, 
tasteless and inodorous. It is heavier than atmospheric 
air in about the ratio of 11 to 10. In its chemical pro- 
perties it differs widely from air, as will be indicated 
by the following experiments. 

Fill a small jar or a tumbler with this gas, and hav- 
ing covered its mouth with pasteboard, place it with the 
Fig. 2. mouth upward. Remove the pasteboard and 
introduce an extinguished candle, (fire still re- 
maining in the wick,) it will be instantly relight- 
ed, with a slight report, (Fig. 2.) If the gas is 
pure, this can be done several times in succes- 
sion. 

Oxygen then is a supporter of combustion. 
This property can be illustrated more brilliantly 
by another experiment. A piece of lighted phos- 
phorous placed in a jar of oxygen, burns with a light so 
brilliant, that it is insupportable to the eye. A piece 
of charcoal ignited and placed in a vessel of this gas, 
burns rapidly, throwing off" bright scintillations. 

Its power to support combustion is not confined to 
those substances which we call combustibles, but many 
substances which are generally considered incombusti- 
ble, are burned rapidly and with brilliant effect in oxy» 
gen. 

What is collected in the inverted jar? What is said of the physical 
properties of this gas % In what ratio is it heavier than air? How is it 
shown that oxygen is a supporter of combustion ? What different sub- 
stances will burn brilliantly in oxygen ? 





OXYGEN. 1^0 

Zinc, iron and steel wire, the diamond and other 
things called incombustible, are consumed if the tem- 
perature is sufficiently raised before they are placed in 
the gas. 

To prepare the iron wire for burning in oxygen, it 
should be coiled about a small cylinder to give it a 
proper shape, and the end dipped in melted suU Fig. 3. 
phur. The sulphur is ignited, and the coil pla- 
ced in the bottle of gas, as in (Fig. 3.) A fine 
watch spring arranged in this way burns bril-l 
liantly, throwing off a shower of sparks. 1 

Such is the heat of the globules of melted 
matter that drop off during the combustion of! 
the iron wire, that after passing through a considerable 
portion of water in the bottle, they melt the glass, and 
are embedded in it. 

The bottle in which the experiment is tried, should 
contain 2 or 3 inches depth of water to prevent its de- 
struction by these globules. The cork to which the 
spiral wire is attached should fit loosely in the bottle. 

Oxygen is not only a supporter of combustion in the 
experiments here given, but is the great supporter of 
combustion wherever it goes on. Supplied from the 
atmosphere, it feeds the fires of the furnace and the 
forge, the flame of the lamp and the gas light. Even 
the animal frame is warmed by a kind of combustion 
within, carried on by means of oxygen. 

If a bird be placed in a confined portion of oxygen 
gas, it will live five or six times as long, as in the same 
volume of atmospheric air. It is, therefore, a supporter 
of animal life. If blood be agitated in oxygen, it 
changes to a bright vermillion color, and the same 
change is effected by the oxygen of which the air is in 

Describe the experiment with a steel watch spring. Does ordinary 
combustion depend upon the presence of oxygen ] Whence is it supplied ? 
How is it shown that oxygen is a supporter of animal life 1 What is the 
effect of oxygen upon hlood, agitated in a vessel of this gas ? 



20 



AGRICULTURAL CHEMISTRY. 



part composed, in the blood of living animals. This is sup- 
posed to be the cause of animal heat ; the nature of the 
change will be mentioned hereafter more particularly. 

Oxygen appears to exist nowhere in nature in a dis- 
engaged state, but in a combined state it is more gene- 
rally diffused than any other element. 

It constitutes eight ninths of the water upon the sur- 
face of the earth, one fifth of the surrounding air, more 
than one third of the mineral crust of the globe, more 
than one half of ail animal substances, and nearly one 
half of the vegetable forms growing upon the face of the 
earth. 

This gas is absorbed by water ; 100 measures ot the 
latter taking up 6 | of oxygen. 

Oxygen acts an important part in the production of 
vegetable forms, but this is not the proper place to en- 
ter into an examination of its influence upon plants. 
This part of the subject is deferred until the pupil is 
supposed to understand the nature of some of the more 
important compounds of Oxygen with other elements. 

The process given for obtaining this gas, is not the 
one usually adopted, but it is given here on account of 
the simplicity of the changes connected with it. 

Fig. 4. 




What is the effect of this change when it is produced in the animal 
system ? What proportion of water and air, also mineral, animal and 
vegetable substances, does oxygen constitute ? 




HYDROGEN. 21 

A more economical method for obtaining oxygen is 
represented by (Fig. 4.) A substance, known as black 
oxide of manganese, is introduced into an iron bottle, to 
which an iron tube (&) is fitted. The conducting tube 
(c) is connected by means of a tube of india-rubber, (e.) 
The bottle arranged in a furnace as represented in the 
f]jg:ure, is made red hot, and oxygen is disengaged in the 
bottle, and collected in the jar. A common gun-barrel 
may be used instead of a bottle, where small quantities 
only are required. 

Fig. 5 represents another process 
for obtaining loxygen. The flask 
{a) contains a mixture of black oxide 
of manganese and oil of vitriol, two 
parts of the former to one of the lat- 
ter. By the application of heat, 
oxygen is generated, and is collect- 
ed as in the preceding processes. 

If a substance called chlorate of potash be mixed with 
the manganese, instead of oil of vitriol, the gas will be 
obtained much more easily and rapidly ; if this mixture 
be used, an iron bottle or gun-barrel may be substituted 
for the flash, and arranged as in Figure 4. 

Hydrogen, H= 1 . 

In (Fig. 6,) we have a retort (a) containing water, 
connected with an iron tube, (cc.) This tube is filled with 
iron wire, and kept at a red heat by a furnace. If we ap- 
ply the heat of a spirit lamp to the retort until the water 
boils, bubbles of gas will begin to appear, rising from 
the end of the connecting tube and filling the jar. This 
gas is called Hydrogen, and like Oxygen, is an element. 
It is colorless, transparent, and when pure, inodorous. 

Give other processes for obtaining oxygen What is the symbol for 
hydrogen? Its atomic weight? Describe the process for obtaining it? 
What are its properties ? 



22 



AGRICULTURAL CHEMISTRY. 
Fig. 6. 




Fig. 7. 



It is absorbed by water in very small quantity, 100 
measures of water absorbing only l^ of hydrogen. 

The most striking physical property of this gas is its 
extreme lightness, being 200,000 times lighter than Mer- 
cury, and 14 times lighter than common air. This 
property renders the gas applicable to aerostatic pur- 
poses, and balloons are generally inflated with it. 

The principle of balloons is aptly il- 
lustrated by blowing soap bubbles by 
means of a bladder filled with hydrogen, 
and a tobacco pipe, as represented in 
(Fig. 7.) The bubbles will rise rapidly 
through the air, and if a lighted candle 
be applied, the gas will burn with a 
yellowish flame. Here we discover a 
new property of hydrogen — its inflammability. 

If a jar of this gas be held with the mouth down- 
wards, (on account of the levity of the gas,) and a light- 
ed candle be immersed in it, the gas will be fired at the 
surface, and the candle will be extinguished in its pas- 
sage into the jar, and relighted again at the surface as 
it is withdrawn. By this experiment, we are made ac- 
quainted with another property of hydrogen — it is a 

What is said of its lightness? For what purposes is it used on account 
of its lightness 1 How is this illustrated 1 If a lighted candle be applied 
to the rising bubbles, what will be the result ? What is the effect when 
a lighted taper is introduced into an inverted jar of hydrogen 1 





HYDROGEN. 23 

non-supporter of combustion. It will not burn unless 
oxygen be present. If we make a mixture of hydrogen 
and air — 2 volumes of the former and 5 of the latter— 
and, confining it in a strong tube, fire it by applying a 
lighted taper to a small aperture, a violent explosion 
will take place. 

When a jet of hydrogen is burned at the Fig. 8. 
extremity of a small tube, musical sounds can 1 
be produced by covering the flame with a .^^'^^ 
large tube of glass or metal, as in (Fig. 8.) ' 

These tones are occasioned by the rapid 
succession of slight explosions within the tube, 
which produce a vibratory movement of the 
air. 

In this experiment the gas is obtained by 
placing in the bottle fragments of zinc, or iron 
filings, and pouring on a mixture of one part 
of oil of vitriol, and three of water. The jet should not be 
ignited until the air is expelled from the bottle lest an 
explosion ensue. The musical 
tones may be varied by moving ^^' 

the tube up or down, or by ta- 
king tubes of different sizes. 
Hydrogen is UKSually obtained 
by the action of dilute oil of 
vitriol upon zinc or iron, as in 
the experiment with the jet, and 
the apparatus may be arranged 
as in (Fig. 9.) 

It is a non-supporter of respiration, although it does 
not prove instantly fatal when inhaled. This gas is not as 
extensively diffused as oxygen, constituting but a small 
proportion of the mineral crust of the globe, one ninth of 
water, and from 5 to 7 per cent, of vegetable substances. 

What is the consequence of firing a mixture of hydrogen and air con- 
fined in a tube 1 How may musical tones be produced 1 How are they 
occasioned] How is hydrogen usually obtained ? Will it support res- 
piration 1 To what extent is it a constituent of plants? 




24 



AGRICULTURAL CHEMISTRY. 




Nitrogen. N— 1 4. 

Fig- 10. Place a float upon the surface 

of the water in the cistern ; lay 
a piece of phosphorus upon it, 
and having ignited, place an 
empty jar over it as in (Fig. 10.) 
As the phosphorus burns, white 
fumes will fill the jar, and the 
water will rise and occupy one 
fifth o-f the space, at first occu- 
pied by air. The white fumes 
will disappear in a short time, and leave a colorless gas 
called Nitrogen. It is devoid of taste or smell, and 
sparingly soluble in water — about the same as hydrogen 
in this respect. 

Nitrogen is lighter than air in the ratio of 97i to 100. 
A lighted candle immersed in this gas is immediately 
extinguished. Animals die in it, not from any poison- 
ous quality of the gas, but on account of the absence of 
oxygen. From its incapability of supporting life, it is 
called azote, A moistened mixture of iron filings and 
sulphur may be substituted for the phosphorus in the 
process given, but a considerable length of time is re- 
quired in this case, for effecting the required result. 

This gas is an essential constituent of the atmosphere, 
forming about 80 per cent, of its bulk— does not occur 
in the mineral masses of the earth in any notable quan- 
tity, but forms a part of many animal and vegetable 
substances, and probably exerts a very important influ- 
ence in the organization of plants. 

How is nitrogen obtained 1 Describe its appearance and properties. 
How much lighter than air? Its effect upon flame and animal life? 
What may be substituted for phosphorus in the process for obtaining ni- 
trogen? What proportion of the atmosphere does this gas constitute? 
What influence does it exert in the vegetable world ? 



CARBON — SILICON. 25 

Carbon. 0=6. 

When wood is burned without free access of air, a 
substance called charcoal is produced. This charcoal 
consists of carbon, with a slight admixture of earthy 
matter. This form of carbon is light and porous, but 
other forms occur, such as plumbago, (black lead,) and 
the diamond, which are much denser. Newly prepared 
charcoal possesses the peculiar property of absorbing 
in large quantity, the moisture and various gases con- 
tained in the atmosphere. Its importance as a fertilizer 
seems to depend in a great measure, upon this property. 

Carbon is an essential ingredient in all animal and 
vegetable substances, forming from 40 to 50 per cent, 
of the latter, and is found every where in air, sea, and 
earth, in combination with other elements. 

Charcoal when applied to soils greatly promotes 
vegetation ; not principally however, by supplying 
nourishment from its own substance, for it can not im- 
mediately enter the roots of plants, but as a medium 
through which many necessary gaseous constituents are 
conveyed to the plant. 



SECTION III. 

SILICON, SULPHUR, PHOSPHORUS, CHLORINE, 
IODINE, BROMINE, FLUORINE. 

Silicon. Si=22. 

Silicon is a dull brown powder, obtained from silica 
by an intricate and difficult process. Silica is a com- 

What is charcoal ? What other forms of carbon are mentioned ? 
What important property does newly prepared charcoal possess ? To 
what extent is carbon a constituent of plants ? How does charcoal pro- 
mote the growth of plants ? Describe silicon 1 



26 AGRICULTURAL CHEMISTRY. 

pound of oxygen and silicon, and is familiar to all un- 
der the forms of sand, quartz, flint, &c. Silicon when 
heated in the open air, takes fire on account of the union 
of oxygen with it, and forms silica again. 

This element constitutes about one sixth of the 
mineral crust of the earth, and is always found com- 
bined with oxygen. 

The compound silica is devoid of color, taste or smell, 
and is infusible except by the strongest heat. It is one 
of the most abundant substances constituting a portion 
of almost all soils, and occurs in the ashes oi all plants. 

Sulphur. 5=16. 

This elementary substance is too well known to re- 
quire a description. The sulphur of commerce is ob- 
tained from the craters of volcanoes. It is brought up 
or sublimed by heat, and condenses in the fissures of 
the crater. Sulphur is heavier than water in the ratio 
of 199 to 100. It is found very extensively combined 
with the different metals, and is a constituent of animal 
and vegetable substances. It is insoluble in water, and 
is met with under three different forms : flowers of sul- 
phur, lac sulphuris, and roll brimstone. 

Although a constituent of plants, sulphur does not 
exert any very important influence, in its uncombined 
state, upon vegetation. 

Phosphorus. P=16. 

Phosphorus is a solid, usually of a pale yellow color, 
but when pure, transparent and colorless. At ordinary 
temperatures it is of the consistence of wax, but at a 

What is silica 1 What different forms of silica are mentioned ? How 
is silicon converted into silica 1 Whence is the sulphur of commerce ob- 
tained ? How much heavier than water is it ? Does it exert an impor- 
tant influence in its uncombined state 1 



CHLORINE. 



27 



low temperature is brittle. It is not found in an uncom- 
bined state, but is obtained from bones by the following 
process. 

The bones are burned and then reduced to powder. 
This powder is acted upon by oil of vitriol diluted with 
water, the resulting mixture is strained, and the liquid 
part mixed with powdered charcoal. This mixture 
when dry is introduced into an earthen retort, and sub- 
jected to a high heat. The retort should have a tube of 
copper attached, which should pass beneath the surface 
of water. The phosphorus distilling over, condenses in 
the copper tube and flows down into the water. 

Phosphorus is highly inflammable, and burns slowly 
at ordinary temperatures when exposed to the air. It 
takes fire and burns rapidly when heated slightly, and 
is readily inflamed by friction. It should be preserved 
in well stopped bottles, under water. If kept in the 
dark it will remain colorless, but exposed to the light, 
becomes red. 

Phosphorus is found in nature, chiefly in the animal 
kingdom as a constituent of bones, but is contained also, 
in small quantity, in vegetable forms, and is a constitu- 
ent of some minerals. Phosphorus is heavier that water 
in the ratio of 177 to 100. 

Chlorine, CZ=36. 

If into a glass flask, we introduce a mixture of com- 
mon salt three parts, and a substance called the black 
oxide of manganese one part, and pour upon it two parts 
of oil of vitriol ; by the application of heat, a greenish 
yellow gas will be produced. This is called chlorine. 
It has an exceedingly pungent, disagreeable odor, and 

Describe phosphorus. Give the process for obtaining it ? What is 
said of its inflammability 1 Where is it chiefliy found ? How much 
heavier than water? By what process is chlorine obtained ? What is 
its color 1 Its properties ? 




28 AGRICULTURAL CilEMISTRY. 

extinguishes a lighted taper ; there are certain substan- 
ces, however, which take fire spontaneously in this gas, 
phosphorus, gold leaf, arsenic, &:c. 

As chlorine is more than 4 times as heavy 
J^'.^ ' as atmospheric air, it can be collected in 
.an open vessel with the mouth upwards, as 
represented in (Fig. 11.) It can not be 
collected over water, because this fluid ab- 
sorbs twice its own bulk of the gas. 

Chlorine exists in large quantity, com- 
bined with another element, forming vast deposits ot 
rock salt ; it is also a constituent to some extent, of ani- 
mal and vegetable forms. 

A solution of chlorine in water, is said to hasten the 
germination of seeds. 

Chlorine is remarkable for its great bleaching proper- 
ties, and is used, in a state of combination with lime, for 
discharging colors. 

Iodine. 7=126. 

Iodine is a bluish black solid, with a lustre somewhat 
metallic. It is obtained from the ashes of sea weed, 
sponge, &c. ; but as it does not occur in any of the 
plants cultivated for food, we shall not dwell upon it 
here. It is concerned only in the production of mainne 
plants. 

Bromine. Br=lS. 

Bromine is a liquid of a blood-red color, and pungent 
disagreeable odor. It may be obtained from sea 
water, sea weeds, and brine springs. Like chlorine, it 

What substances take fire in it spontaneously? How can it be col- 
lected % What is the effect of a solution of chlorine in water upon seeds ? 
For what is chlorine remarkable ? What is the atomic weight of iodine 1 
Describe this element. In what plants does it occur ? What is the 
symbol of bromine ? Describe this element. 



fLUORINE POTASSIUM. 29 

possesses bleaching properties, and will support the 
spontaneous combustion of certain metals. Like Iodine, 
it is concerned in the formation of marine plants only. 

Fluorine, F=18. 

The element to which the name fluorine has been ap- 
plied, is somewhat imaginary, that is, it has never been 
isolated, although its existence has been rendered ex- 
ceedingly probable. It occurs in several minerals, and 
in the teeth of animals. It has been recently ascertain- 
ed that it is a constituent of the ashes of plants. 

We shall consider it farther hereafter in its combined 
state. 



SECTION IV. 

POTASSIUM, SODIUM, CALCIUM, MAGNESIUM, IRON, 
MANGANESE. 

Potassium, jK'=40. 

This element is a metal, and can be obtained by the 
following process. A mixture of potash and coarsely 
powdered charcoal is introduced into an iron bottle, and 
the bottle connected by means of a tube, with a vessel 
of naptha. Subjecting this to a white heat, the metal 
distils over, and condensing in the receiver in the form 
of globules, is protected by the naptha. 

At common temperatures, potassium is soft like wax, 
its color bluish white. It is lighter than water in the 
ratio of 86| to 100, and has such an avidity for oxy - 

In what respect is it similar to chlorine ? What is the atomic weight 
of fluorine 1 Where does it occur? What has been recently ascertam- 
ed? Give the symbol and atomic weight of potassium. How is it ob- 
tained 1 Describe it. 

*2 




30 AGRICULTURAL CHEMISTRY. 

gen that it will unite with it if exposed to the air ; it is 
necessary, therefore, to preserve it in a fluid that con- 
tains no oxygen— naptha is the substance used for this 
purpose. 

Fig^^2^ If a piece of potassium be thrown upon 
"^" water or upon ice, it will take fire, and burn 
with a pink flame, (Fig. 12.) This element 
^is found in combination with other substan- 
ces in the ashes of plants. 

Sodium. Na~24. 

If we repeat the process just given for obtaining po- 
tassium, substituting soda in the place of potash, a silver 
white metal will be obtained which is called Sodium. 
It is soft at ordinary temperatures, and lighter than wa- 
ter in the ratio of 93i to 100. 

If thrown upon water, and prevented from moving 
about, it will burn with a beautiful yellow flame. It 
must be preserved in naptha to prevent its uniting with 
oxygen. Sodium does not occur in its elementary state 
in nature, but in combination with chlorine, forms ex- 
tensive deposits of rock salt ; it is found also in the ashes 
of plants, and in union with other elements, as a con- 
stituent of many soils. 

Calcium, Ca=20, 

Calcium is obtained with great difficulty, and there- 
fore has never been formed in sufficient quantity to 
allow a proper examination of it. It is a silver white 
metal, and is obtained from lime, which is a compound 
of oxygen and this metal. Thus combined, it consti- 

Why is it necessary to preserve it in naptha ? How is sodium obtain- 
ed? Describe it. Describe the effects of potassium and sodium when 
thrown upon water. What does sodium form by its combination with 
chlorine ? Sodium is a constituent of what ? Describe calcium. 



MAGNESIUM IRON MANGANESE. 31 

.utes a large portion of the mineral crust of the earth ; 
it is also a constituent of the bony frame-work of ani- 
mals, and is found in the ashes of plants. 

Magnesium, Mg=l2, 

From magnesia, a white metal called magnesium is 
with difficulty obtained. If it be heated to "i^edness it 
takes fire, uniting with oxygen and forming magnesia 
again. 

It does not occur in nature in its elementary form, 
but combined with oxygen, is a constituent of many 
minerals and is found in the ashes of plants. 

Iron. Fe=28. 

It is hardly necessary to describe this element, since 
its appearance and properties are, in some degree, fa- 
miliar to all. Its various applications in the arts render 
it more indispensable than any other element. Iron is 
found native, or uncombined in considerable quantities, 
yet most of the iron of commerce is obtained from com- 
pounds of oxygen with this metal. It is a constituent 
of plants and soils. 

Manganese. Mn—2S. 

If we take the black oxide of manganese, and mixing 
it with lamp black and oil, subject it to the highest heat 
of a smith's forge, we shall obtain a grayish white 
metal, which is manganese. 

It is eight times as heavy as water, very brittle and 

From what is it obtained? Calcium combined with oxygen consti- 
tutes what ] Give the symbol and atomic weight of magnesium. Whence 
is it obtained 1 Does it occur in its metallic form 1 Give the atomic 
weight of iron. From what is most of the iron of commerce obtained ? 
What symbol is written instead of manganese ? What is the atomic 
weight of manganese 1 How is it obtained ? 



32 AGRICULTURAL CHEMISTRY. 

exceedingly infusible. It does not occur native, but is 
widely diffused in combination with oxygen, being a 
constituent of most soils, although in small quantity. 
Traces of it are found in animal and vegetable sub- 
stances. 

Aluminunu ^Z=14. 

This metal is obtained with great difficulty, never oc- 
curring in nature in the metallic form. In combination 
with oxygen, is the principal ingredient of all clays. 
In this form, it is also a constituent of many rocks and 
most soils, and exists in small quantity in the ashes of 
plants. 

We have now examined successively, the 18 elements 
which enter into the constitution of plants. In doing so 
we have purposely avoided saying much concerning 
the part each element acts in the production of the 
plant, because this part of the subject requires a know- 
ledge of certain compounds hereafter to be explained. 
Few of the elements enter into the circulation of the 
plant, in their elementary forms. They usually unite 
with each other in various proportions, and from the 
combinations thus formed, the plant obtains its nourish- 
ment. 

Does it occur in the metallic state ? With what is it found in combi- 
nation? It is a constituent of what] What symbol represents alumi- 
num? Its atomic weight ? Is it found in the metallic form? When 
Combined with oxygen, what is it a principle ingredient of? From what 
sources are the various elements supplied to the plant. 



PART IL 

PRIMARY COMPOUNDS. 



The eip;hteen elementary substances described in the 
preceding pages, combine with each other in various 
proportions, forming a class of substances called 'pri- 
mary compounds. 

The following list contains all of these that are of 
interest to the agriculturist. 

The column of Symbols shows what elements are 
united, and in what proportion, to form the different 
compounds. H O signifies the combination of Hydro- 
gen and Oxygen. N Os represents the union of Nitro- 
gen and Oxygen ; the 5 indicating that there are five 
proportions or atoms of oxygen to one of nitrogen. 
There are five different compounds of these two ele- 
ments— NO, NO2, N03,N04, and NO5, but none 
of them are of any importance connected with this de- 
partment of chemistry, except the last. In the column 
marked equivalents, we have the combined atomic 
weights of the elements which form the compound. 

The atomic weights of oxygen and hydrogen are 
8 and 1, therefore, when united to form water, the equiv- 
alent number is 9. In the compound, N O5, we have 
one atom of Nitrogen — weight 14, and 5 atoms of Oxy- 
gen— weight 5X8=40 ; these numbers united give 54 

Of what does Part IL treat 1 How are the primary compounds form- 
ed '? What is the signification of H in the table ? Of N 5 ? How 
are the five compounds of oxygen and nitrogen expressed symbolically ? 
"Whence are the numbers of the column marked equivalent, derived ? 
Why is 9 the equivalent of water? Why is 54 the equivalent of nitric 
acid? 



u 



AGRICULTURAL CHEMISTRY. 



as the equivalent of Nitric Acid. This general law is 
observed with respect to the union of elements in dif- 
ferent proportions. If an element combines with ano- 
ther to form different compounds, the number for that 
element in the higher combinations will be multiples of 
its number in the lowest. 

Table of Frimary Compounds. 



Names. 


Common Names, 


Symbols. 




Protoxide of Hydrogen, 


Water, 


H 


9 


Nitric Acid, 


Aqua Fortis, [monia, 


N O5 


54 


Ammonia, 


With water. Aqua Am- 


NH3 


17 


Carbonic Acid, 


Fixed Air, 


CO2 


22 


Silica or Silicic Acid, 


Flint, Sand, &c. 


SiOs 


46 


Sulphurous Acid, 




SO2 


32 


Sulphuric Acid, 


Oil of Vitriol, 


S O3 


40 


Sulphuretted Hydrogen, 




S H 


17 


Phosphoric Acid, 




P2O5 


72 


Hydrochloric Acid, 


Muriatic Acid, 


H CI 


37 


Hydrofluoric Acid, 




HF 


19 


Protoxide of Potassa, 


Potash, 


KO 


48 


Protoxide of Sodium, 


Soda, 


NaO 


32 


Chloride of Sodium, 


Common Salt, 


NaCl 


60 


Protoxide of Calcium, 


Lime, 


CaO 


28 


Chloride of Calcium, 




CaCl 


56 


Fluoride of Calcium, 


Fluor Spar, 


CaF 


38 


Magnesia, 




MgO 


20 


Protoxide of Iron, 




FeO 


36 


Peroxide of Iron, 


Iron Rust, 


FesOs 


80 


Protoxide of Manganese, 




MnO 


36 


Deutoxide of Manganese, 


[ese, 


Mna O3 


80 


Per oxide of Manganese, 


Black oxide of Mangan- 


MnOa 


44 


Alumina, 


Clay, (impure) 


AI2O3 


52 



NAMES. 



It will be seen by referring to the table, that oxygen, 
in uniting with different elements, produces two kinds 
of compounds — oxides and acids. 

The term acid signifies sour or sharp, and is applied 
to those compounds of a sour, biting character, which 



What two classes of compound does oxygen form by its combinations ? 



NAMES. 35 

have the power of changing most vegetable blue colors 
to red. If two acids are fornaed by the union of oxy- 
gen with one element, the name of the one which con- 
tains most oxygen, is formed by uniting the termination 
of ic to the name of that element that which has less by 
adding ous to the same. Thus sulphuric acid has three 
proportions of oxygen, sulphurous acid only two. Some- 
times there are three acids, and in that case, the one 
which has least oxygen, forms its name by prefixing the 
syllable hypo to the name of the acid ending in ous : 
thus, we have another acid from sulphur and oxygen 
called hyposulphurous acid, containing one proportion 
of oxygen and one of sulphur. 

The name oxide implies the union of oxygen with an 
element, but not in sufficient quantity to produce 
an acid. If there are several different oxides, the 
names are formed by prefixing the contracted Greek 
numerals, prot, deut and trit, signifying first, second and 
third. In this way we apply the name protoxide to the 
compound having the least oxygen, the compound con- 
taining an additional proportion of oxygen, is called 
deutoxide, &c. The Xexvn peroxide is usually applied 
to the compound containing most oxygen, whether it 
contain two, three, or four proportions. In the com- 
pounds of oxygen and nitrogen referred to, we have 
both oxides and acids. 

Protoxide of Nitrogen, N O =22 

Deutoxide of Nitrogen, N O ^ =30 

Hyponitrous Acid, N 03=38 

Nitrous Acid, N 0^=46 

Nitric Acid, N 0^=54 

"What is the meaning oi acid, and to what compound is this name ap- 
plied ■? What is the rule for the terminations of the different acids 1 
What does the name oxide signify 1 How are the names for different 
oxides formed 1 To what is the term peroxide applied 1 Name the dif- 
ferent compounds of oxygen and nitrogen, and give their symbols and 
equivalents? 



36 AGRICULTURAL CHEMISTRY. 

The word oxygen signifies generator of acids, and u; 
the time this name was applied, oxygen was considered 
the universal acidifying principle. This was a mistake. 
It will be seen that two of the acids given in the table 
are formed without the aid of oxygen, as are others not 
given in this connection. 

We shall now consider each of the primary com- 
pounds with its bearing upon the process of vegetation. 

PROTOXIDE OF HYDROGEN, OR WATER. 

H 0=9. 

We have already shown the properties of oxygen 
and hydrogen vi^hen examined separately. If these two 
gases be united in the proportions of two volumes of the 
latter to one of the former, or by weight, 1 of hydro- 
gen to 8 of oxygen, a colorless liquid is produced with 
which all are familiar, under the name oi water. This 
compound will not be formed by merely mixing the two 
gases in proper proportions. But if a lighted taper be 
applied to the mixture, the gases unite with a loud ex- 
plosion, and water is the result. 

Soap bubbles filled with this mixture, may be explo- 
ded while rising slowly through the air. In the explo- 
sion of the mixture of hydrogen and air, (p. 22,) water 
is produced by the union of the oxygen of the atmos- 
phere with hydrogen. The same result is produced in 
the production of musical tones ; the water accumulating 
upon the sides of the tube. 

The elements of which water is composed exist in 
plants, forming from 35 to 50 per cent, of their weight. 

What does the word oxygen signify? Is it the only generator of 
acids '? What is the chemical name of water 7 What is the result when 
a mixture of oxygen and hydrogen is fired? To what extent do oxygen 
and hydrogen exist in plants 1 



OF THE ATMOSPHERE. 37 

Nearly all the hydrogen which plants contain, is sup- 
plied by the decomposition of water. 

Most of the oxygen of the plant is without doubt, de- 
rived from the same compound, but this element may 
readily be obtained from several different sources. 

These two elements, oxygen and hydrogen, do not 
exist in plants in just the proportions to form water, hy- 
drogen being generally in excess. 

All plants contain a quantity of water undecomposed. 
It forms i by weight of all newly gathered vegetable 
substances, but is not taken into consideration in esti- 
mating the constituents of plants. Water has the pow- 
er of dissolving solid substances, and absorbing gases, 
thus acting as a medium through which food is convey- 
ed to the plant. In this way it acts a most important 
part in vegetation, and will be more fully treated of 
hereafter. 

OF THE ATMOSPHERE. 

Atmospheric air is a mixture of the gases oxygen and 
nitrogen, in the proportion by volume of 21 of the for- 
mer to 79 of the latter. It contains other gases in very 
small quantity. 

The constitution of air is found to be nearly the same 
in all places and at all heights above the surface of the 
earth. Gay Lussac experimented upon air brought 
down from a height of more than 21,000 feet, to which 
he had ascended in a balloon, but its constitution was 
identical with that of the air of lower regions. 

The atmosphere terminates at a height from 40 to 
.50 miles above the surface of the earth. It is not neces- 

Whence is obtained the hydrogen of plants 1 What else is derived 
mostly from the same source 1 How much water in newly gathered 
vegetables'? What property has water that renders it very beneficial to 
the plant ? What is the composition of atmospheric air 1 Is it the same 
in ail localities ? The height of the atmosphere 1 



S8 AGRICULTURAL CHEMISTRY. 

sary to examine all the physical properties of air— its 
pressure — elasticity, &c., as they have no direct bear- 
ing upon this department of chemistry. 

It is the oxygen of the air which renders it capable 
of supporting respiration, yet the nitrogen is required 
for the purpose of tempering or reducing the oxygen. 
If an animal be placed in an atmosphere of pure oxy- 
gen, the vital functions are excessively stimulated ; the 
circulation of the blood is quickened, fever is induced, 
and the system is soon prostrated ; nitrogen serves 
merely to dilute the oxygen. 

Water has the povsrer of absorbing the constituent 
gases of air, and it is possible that by this means these 
elements are conveyed into the circulation of plants, 
yet it is more probable that the oxygen and nitrogen of 
plants are derived from other sources. Atmospheric 
air is not a chemical compound, but a mere mixture of 
its constituent gases. 

NITRIC ACID, OR AQUA FORTIS. 

N 05=54. 

Although under ordinary circumstances, the oxygen 
and nitrogen of the atmosphere do not unite to form a 
chemical compound, yet w^henever thunder showers 
occur, these elements are brought together and form 
nitric acid, (aqua fortis.) This acid carried to the soil 
unites with different substances, and sometimes forms 
extensive deposites of nitrogenous compounds. In this 
way a quantity of saltpetre is formed in the East Indies 
sufficient to supply all Europe. 

Nitric acid is without doubt absorbed by the plant, 

What would be the consequence were there no oxygen in the atmos- 
|)here 1 Are the oxygen and nitrogen of the plant derived from the at- 
mosphere 1 Under what circumstances is nitric acid formed 1 Is it ab- 
sorbed by the plant ? 



AMMONIA. 30 

since it is found in the juices of many living vegetables. 
The tobacco plant contains it, probably in combination 
with potash. This will be indicated when the stalks 
of the plant are ignited; they will burn like paper that 
has been dipped in a solution of saltpetre. 

Nitric acid applied to the young plant, greatly facili- 
tates its growth, and the grain derived therefrom is 
usually nutritious in its quality. It is not appUed in 
the acid form, but in combination with other substances. 
These compounds will be spoken of hereafter. Nitric 
acid is without doubt one source from which plants ob- 
tain the nitrogen which enters into their constitution, 
but as there is a very limited quantity of the acid form- 
ed in most soils, a supply of nitrogen must be ensured 
from other sources, one of the principal of which is the 
following compound. 

AMMONIA. 

NH3=17. 

Ammonia is a gaseous compound, consisting of nitro- 
gen and hydrogen, united in the proportion of one atom 
of the former to three of the latter, 14+3=17 the 
equivalent number for ammonia. If we pulverize sal- 
ammoniac, mix it with an equal quantity of slacked lime, 
and add water sufficient to form it into a paste ; by ap- 
plying heat, ammonia will be produced. It is a colorless 
gas, of an exceedingly pungent and irritating odor, and 
lighter than atmospheric air in the ratio of 59 to 100. 

Water absorbs this gas with great avidity, especially 
at low temperatures. At the freezing point it takes up 
780 times its own bulk. Thus dissolved in water, it 

What proof? What is the effect of nitric acid upon vegetation? Is 
it applied in the acid form ? What is said relative to the quantity of this 
acid in soils ? How is ananionia obtained ? How much of this gas does 
water absoit> 2 




40 AGRICULTURAL CHEMISTRY. 

forms hartshorn or aqua ammonia. It was formerly 
obtained mostly from horn, and from this circumstance 
derives its name. 

It is plain that in producing this gas, it can not be 
collected over water, as it would be ab- 
"^^^ sorbed by that fluid ; but since it is much 
lighter than air, it can be collected in an 
inverted bottle or flask, as in (Fig. 13.) 

Ammonia will not support combustion, 
but is itself in a slight degree combustible. 
It is given ofl'in considerable quantity from 
decaying animal substances, and those 
vegetables which contain nitrogen give ofl* 
ammonia in the process of decomposition. 
This gas is a source from which plants probably obtain 
both hydrogen and nitrogen, and is doubtless the prin- 
cipal source from which the latter is supplied to the 
plant. 

Nitrogen, although forming but a small portion of the 
plant, is absolutely essential to the perfect development 
of the most important part of it, and since we are to 
depend principally upon ammonia for a supply of this 
element, it is of the first importance to the agriculturist 
to know in what way this gas is to be supplied to the 
plant. 

It is exceedingly volatile, and if existing in the soil 
in an uncombined state, will soon pass off" without bene- 
fiting the plant. It is brought down by every shower, 
havmg been absorbed by the rain from the atmosphere, 
and unless it is immediately united with some substance 
that has the power of retaining it or rendering it fixed, 
its volatility will cause it to disappear, and become 
again a part of the atmosphere. 

What name is applied to water saturated with ammonia 1 How may 
this gas be collected? Whence is ammonia derived? What does it 
supply to the plant ? Why is it important that this gas should be re- 
t ained in the soil ? 



AMMONIA. 41 

If nitric acid is formed at any time in the air, this 
probably unites with the ammonia, as will be shown 
hereafter. 

Certain substances may be supphed to the soil that 
Jiave the power of fixing volatile ammonia, and retain- 
ing it as food for the plant. Perhaps the most impor- 
tant of these is charcoal. We have before seen that 
this substance has the power of absorbing various vapors 
and gases ; it absorbs ammonia to a greater extent 
than any other; one cubic inch of newly prepared 
charcoal absorbing ninety inches of the gas. 

Ammonia is called an alkali. This term is applied to 
those compounds that have the power of neutralizing 
the different acids, restoring colors that have been 
changed to red by the same, and of changing some 
vegetable colors to green. 

Not only is ammonia necessary for the purpose of 
supplying the elements of which it is composed to the 
plant, but it is believed to be itself, a constituent of 
vegetable forms ; for it has been detected in the leaves 
of the tobacco plant and others ; while some plants ac- 
tually give off ammonia from their leaves or flowers, 
Jt \s probable then that this gas is absorbed by the plant 
without decomposition, although this is by no means 
certain. Whatever the form may be in which it enters 
the plant, it is well determined that ammonia greatly 
facilitates the growth of vegetables. The following are 
some of Johnston's reasons for supposing that ammonia 
enters directly into the circulation of plants. 

" It is proved, by long experience, that plants grow 
most rapidly and most luxuriantly when supplied with 
manure containing substances of animal origin. These 
substances are usually applied to the roots or leaves in 

How may this be accomplished ? What is said of the power of char- 
coal to absorb ammonia ? Why is this gas called an alkali ? What rea- 
son is there for believing that ammonia in its compound form is a con- 
stituent of plants ] 
*2 



42 AGRICULTURAL CHEMISTRY. 

a state of fermentation or decay, during which they al- 
ways evolve ammonia. Putrid urine and night soil are 
rich in ammonia, and they are among the most effica- 
cious of manures. This ammonia is supposed to enter 
into the circulation of plants along with the water ab- 
sorbed by their roots, and sometimes even by the pores 
of their leaves. We can scarcely be said to have as 
yet obtained decisive proof that it does so enter, but 
probabilities are strongly in favor of this supposition ; 
and when we consider minutely the mode in which it 
is like to act, when within the plant, we find the proba- 
bihties derived from practical experience to be strength- 
ened by the deductions of theory." 

CARBONIC ACID. 

C 02=22. 

When Hmestone is exposed to a high degree of heat, 
as in the lime-kiln, a colorless gas is given off which is 
called carbonic acid. It consists of one atom of carbon 
united with two of oxygen, and exhibits the properties 
of an acid, inasmuch as it changes certain vegetable 
blues to a red. 

For experiment, it may be obtained from chalk by 
acting upon it in a glass flask or bottle, with oil of vitriol 
diluted with three or four parts of water. It may be col- 
lected over water as oxygen, &c., but on 
account of the power of water to absorb 
it, it is collected without the aid of this 
fluid. Carbonic acid is heavier than air 
in the ratio of 152 to 100; taking advan- 
tage of this property it may be collected in 
an open jar, as represented in the figure. 




What are the views of Johnston ? What symbol represents carbonic 
acid ? What is its equivalent number ? How may it be obtained ? Col- 
lected ? 



CARBONIC ACID. 43 

On account of its great weight it can be poured from 
one vessel to another, and if a lighted candle be placed 
in a tumbler or sQiall jar, and carbonic acid be poured 
from another vessel into this, the candle will be extin- 
guished as if by magic. It is thus proved to be a non- 
supporter of combustion. Carbonic acid is disengaged 
in large quantities in some localities, and is always pro- 
duced during the decay of vegetable substances. It 
is often exhaled from the ground, and accumulates in 
dry wells, vaults, and caverns. Persons have often lost 
their lives by entering wells, &c., which contained this 
gas. Before entering such places, a lighted candle 
should be lowered into the cavity ; if it continues to 
burn, it is a certain indication of the absence of carbonic 
acid. 

Eastern travelers relate that the existence of a cavern 
filled with this gas is a source of profit to some of the 
neighboring natives. 

For the amusement of the stranger, a dog is thrown 
into the chasm ; he soon falls down, to all appearance 
lifeless. The traveler pays for the dog and departs. 
The animal is immediately thrown into water and re- 
covers ; and in a short time is in a condition to die again 
for the benefit of his master and the amusement of trav- 
elers. 

Even diluted with ten parts of air this gas is poison- 
ous, and produces fatal effects if breathed. It is then pre- 
eminently a non-supporter of life. It is this gas that is 
given off" from burning charcoal, and which has so often 
proved fatal to individuals warming small and tight 
rooms by means of coal. In this case the oxygen of the 
air unites with the carbon of which charcoal mostly 
-consists, and produces carbonic acid which occupies 

Describe the manner of extinguishing a candle with this gas. Under 
what circumstances is carbonic acid produced in nature 1 Where does 
It often collect] What precaution should be taken before entering 
vaults, caverns, &c.'? 



44 AGRICULTURAL CHEMISTRY. 

the space before occupied by the oxygen ; thus we 
have an atmosphere made up of nitrogen and carbonic 
acid, both of which are hostile to animal life. 

The process of respiration in a similar way converts 
the oxygen of the air into carbonic acid ; the carbon 
being derived from the blood. This accounts for the 
change produced in blood by immersion in oxygen, 
(page 19.) The union of oxygen with the carbon of 
the blood produces just as much heat as the union of 
the same gas with carbon in the form of charcoal ; 
hence the source of animal heat. 

" The combination ol a combustible substance with 
oxygen," says Liebig, " is, under all circumstances, the 
only source of animal heat. In whatever way carbon 
may combine with oxygen, the act of combination is 
accompanied by the disengagement of heat. It is in- 
different whether this combination takes place rapidly 
or slowly, at a high or a low temperature ; the amount 
of heat liberated is a constant quantity. 

" The carbon of the food being converted into car- 
bonic acid within the body, must give out exactly as 
much heat as if it had been directly burnt in oxygen 
gas or in common air ; the only difference is, the pro- 
duction of the heat is diffused over unequal times. In 
oxygen gas the combustion of carbon is rapid, and the 
heat intense ; in atmospheric air it burns slower and 
for a longer time, the temperature being lower, in the 
animal body the combination is still more gradual, and 
the heat is lower in proportion." 

We have noticed three sources from which carbonic 
acid is given off into the atmosphere, combustion, res- 
piration and the decay of vegetable substances. 

Will carbonic acid support respiration ? What gas is generated by 
burning charcoal 1 What changes are produced by the process of respir- 
ation 1 Will a pound of carbon withdrawn from the blood by respiration 
produce as much heat as a pound of the same element in the form of 
charcoal 1 What is the only source of animal heat ] From what dif- 
ferent sources is carbonic acid supplied to the atmosphere ? 



CARBONIC ACID. 45 

Since these operations have ever been going on and 
must continue as long as fires burn, animals breathe, 
and plants decay, we might reasonably suppose that the 
atmosphere would contain a considerable quantity of 
carbonic acid. By examination, it is found to contain a 
minute quantity, about 2 oV o of its bulk of this gas. We 
have not noticed this in giving the constituent of air 
although it is a constant and all essential constituent. 

It vi^ould be found in greater quantity in the atmos- 
phere were it not that it is taken up by ail growing 
vegetables, its carbon retained, and oxygen returned to 
the atmosphere. It is thus the great source whence is 
derived the carbon of the plant ; this will be rendered 
evident by a few considerations. 

In the first place, carbon being an insoluble solid, 
can not enter directly into the plant ; it must first be 
changed to a liquid or gaseous form. By its union with 
oxygen it becomes a gas, which may be absorbed by 
water, and conveyed into the circulation of the plant 
through the root, or it may be absorbed by the water 
contamed in the tissues of the plant. 

If a spot of sterile land, impoverished by long tillage, 
and destitute of any vegetable matter, or carbon, be 
left undisturbed for* a length of time, it will become 
covered with a growth of various kinds of grasses, 
weeds, shrubs, &c., year by year these die, fall to the 
earth, and become incorporated with the soil, while new 
shoots spring up growing more vigorously than the 
previous ones, and at length like them decay and mix 
with the earth. If this process continue a series of 
years, and then the land be cleared and broken up, it 
will exhibit a black fertile mould, and produce luxuriant 

To what extent does it occur in air? Is it a constant constituent ? 
Whence is derived most of the carbon of the plant? How is it conveyed 
into the circulation of the plant 1 What is the natural process by which 
sterile land frequently becomes productive I 



46 AGRICULTURAL CHEMISTRY. 

crops, where all was barrenness. Whence was ob- 
tained the carbon of the first growth ? for we supposed 
the soil destitute of vegetable matter, — the only visible 
depository of carbon that is available to the plant. It 
must have been obtained from the carbonic acid of the 
atmosphere. The second growth was more luxuriant 
than the first because it could obtain its carbon in part 
from the soil and because the vegetable matter mixed 
with the soil has the power of absorbing the different 
gases that nourish the plant. The accumulation of rich 
black vegetable mould, shows that notwithstanding a 
greater growth each succeeding year. Yet an excess 
of carbonaceous matter was annually deposited in the 
earth. It follows then, that whether the soil contain 
vegetable matter or not, the plant derives most of its 
carbon from the atmosphere. 

Thus we learn that carbonic acid is the great sup- 
porter of vegetable life as oxygen to that of animal. 
Here we discover an instance of adaptation, of unity 
and design, in the natural world, that forcibly impres- 
ses us with the wisdom of that being who has made the 
" circle of eternal change" in the vegetable creation, 
serve to counterbalance the changes produced by ani- 
mal existences, thus ensuring a happy equilibrium. Ani- 
mals are continually vitiating the atmosphere — chang- 
ing its oxygen to carbonic acid. Plants restore the 
equilibrium by absorbing the carbonic acid, retaining 
the carbon and returning the oxygen for the use of ani- 
mals. In the beautiful language of Draper, " The car- 
bonaceous matter which has flowed through the heart 
of man as blood, is transferred, by respiration to the air, 
and aids in the formation of forest trees or painted flow- 
ers. The Asiatics, with whom have originated all the 
varieties of pagan creeds that have spread to any ex- 

If the soil contains a supply of carbonaceous matter will the plant still 
obtain most of its carbon from the atmosphere 1 By what succession of 
changes is the purity of the atmosphere preserved ? 



SILICA, SILEX OR SILICIC ACID. 47 

tent in the world, believed in a transmigration of souls ; 
they would have been much nearer the truth had they 
believed in a transmigration of bodies. The coal that 
we burn is the remains of forests which, in former ages, 
were thronged with living things — forests that sprang, 
as do the trees with us, from gases that were formed 
from the respiration of animals— but of animals that are 
all extinct. 

"Atmospheric air is the cradle of vegetable, and the 
coffin of animal life. Made up as it is, of atoms that 
have once lived, that have run through innumerable 
cycles of change, the aspect of purity it presents con- 
ceals too well its history. In its ethereal expanse are 
crowds of atomic forms that have once blossomed as 
flowers, or participated in the pleasures and pains of 
animal life." {Chemistry of plants, p. 11.) 

SILICA, SILEX OR SILICIC ACID. 

Si 03=46. 

When the element silicon is heated in the air, or in 
oxygen, it burns, and silicia — a compound of oxygen 
and silicon is the result. This compound exists in na- 
ture, completely pure in masses called quartz rock, and 
nearly pure in the various sandstones, sands, flints, (fee, 
it constitutes a portion of most soils and of some a large 
portion ; such are called silicious soils. Silica is infu- 
sible, and devoid of taste or smell, insoluble in water, 
and one of the hardest of minerals. It not only occurs 
in the mass in the sandstones of the earth's crust, but it 
forms by combination with other substances, various 
minerals that occur in different rocks. 

Silica is found in the ashes of plants in great quantity, 

Give the symbol and atomic weight of silica. Where does it exist in 
a state of purity 1 What are those soils called that contain it in large 
quantity] What are its properties? 



48 AGRICULTURAL CHEMISTRY. 

but on account of its insolubility can not be taken up 
by them unless it first combine with other substances. 
Of these combinations we shall speak hereafter ; defer- 
ring any farther remarks upon silica until that time. 

SULPHUROUS ACID. 

S 02=32. 

By burning sulphur in the air or in oxygen, white 
fumes are produced, intensely suffocating, and destruc- 
tive of animal and vegetable life ; this gaseous compound 
is sulphurous acid. 

SULPHURIC ACID, OR OIL OF VITRIOL, 

S 03=40. 

Sulphurous acid is changed to sulphuric acid by the 
following process. Into a leaden chamber containing a 
small portion of water, the fumes of burning sulphur are 
introduced, in connection with those arising from the 
decomposition of nitre,— nitrous acid fumes. The last 
serve as a medium through which oxygen is transfer- 
red from the air to the sulphurous acid, forming an oily 
fluid, which was once named oil of vitriol, but the sci- 
entific name for which is sulphuric acid. This acid 
may be obtained from green vitriol, by first depriving 
it of its water by exposure to heat, and then distilling 
it from a stoneware retort at a high heat. Obtained by 
either of these processes it is not pure sulphuric acid, 
but has combined with it a portion of water. By dis- 
tilling the fluid obtained by the last process, a beautiful 
white crystaline substance is obtained which is the dry, 

' Why cannot pure silica be taken up by the plant ? liow is sulphurous 
acid produced? Of what is it composed ? Give its equivalent number. 
How is this compound changed to sulphuric acid ? How is oil of vitriol 
obtained from green vitriol % How may dry sulphuric acid be obtained % 



SULPHURETTED HYDROGEN. 49 

pure sulphuric acid. It has a great affinity for water, 
and when thrown into it, hisses Jike red hot iron. The 
common sulphuric acid has a great avidity for moisture 
also ; and if a portion be left open to the air it will ab- 
sorb water to such a degree as to double its weight to 
the detriment of its quality. It is exceedingly sour and 
corrosive, nearly colorless when pure, but when any 
vegetable substance has been introduced, the acid chars 
it and becomes discolored. 

Sulphuric acid seldom occurs uncombined ; it is said 
to be contained in small quantity in streams in the vi- 
cinity of volcanoes. This acid is not generally applied 
to soils in its uncombined state. A few successful ex- 
periments have been made however, in which the acid 
was applied in a very diluted state. It occurs combined 
in certain mineral substances, especially in gypsum or 
plaster. Of these compounds we shall speak hereafter. 

SULPHURETTED HYDROGEN. 

S H=17. 

This gas is readily procured by acting upon the sui- 
phuret of antimony (usually called antimony,) with hot 
muriatic acid, in a glass flask. It may be burned 
from a jet as it is formed, as represented in (Fig.-^^^' ^^' 
15.) This gas is given off" in great quantities 
from some mineral springs, and is sometimes used 
in such localities for the purpose of illumination. 
Cold water absorbs it in considerable quantity, 
therefore in collecting it the water must be warm- 
ed or saturated with salt. 

Sulphuretted hydrogen is distinguished by its un- 

What is said of its affinity for water 1 Will sulphuric acid retain its 
strength if left open to the air 1 Describe its appearance and propertied. 
Is it ever applied to soils 1 How is sulphuretted hydrogen procured 1 
Where is it formed in nature ? For what purposes is it sometimes used % 



t 



50 AGRICULTURAL CHEMISTRYo 

pleasant odor. It is this gas that gives to rotten eggs 
their disagreeable smell. With regard to its effect up- 
on vegetation, &c., Johnston says : " Sulphuretted 
hydrogen is exceedingly noxious to animal and vegeta- 
ble life, when diffused in any considerable quantity 
through the air, by which they are surrounded. The 
luxuriance of the vegetation in the neighborhood of sul- 
phurous springs, however, has given reason to believe 
that water impregnated with this gas may act in a bene- 
ficial manner when it is placed within reach of the roots 
of plants. It seems also to be ascertained that natural 
or artificial waters that have a sulphurous taste, give 
birth to a pecuUarly luxuriant vegetation, when they 
are employed in the irrigation of meadows." 

PHOSPHORIC ACID. 

Pa 05=72 

In the process given for obtaining nitrogen, (page 24,) 
the phosphorus unites with the oxygen of the air, in the 
jar producing white fumes. The new compound is 
phosphoric acid, which soon disappears on account of 
its affinity for water. If phosphorus is burned in dry 
air or oxygen gas, this acid is produced in the form of 
snow white flakes. If in this state it be thrown into 
water, it hisses as does dry sulphuric acid under the 
same circumstances. This acid exists in several com- 
pounds hereafter to be described, but does not occur in 
a free state, and therefore is not directly concerned in 
vegetation, in the acid form. 

What does Johnston say with reference to its effect upon vegetation ? 
Why is the chemical equivalent of phosphoric acid 72 1 How is this 
compound obtained 1 What is the effect of throwing the dry acid into 
water ? Is phosphoric acid found uncombined in nature 1 



HYDROCHLORIC ACID, OR MURIATIC ACID. 51 

HYDROCHLORIC ACID, OR MURIATIC ACID. 

H Cl=37. 

If we mix equal proportions of the two gases, hydro- 
gen and chlorine, and expose the mixture to the light, 
the elements will unite and form a gaseous compound 
called hydrochloric acid. If the light be diffuse they 
combine slowly, but if bright sunlight be thrown by 
means of a mirror, upon a glass flask containing the 
mixture, the combination is instantaneous, accompanied 
by an explosion. In this experiment the flask should 
be covered with wire gauze. This compound is ab- 
sorbed by water in large quantities, and the common 
name of the solution is muriatic acid, or spirit of sea 
salt. The gas can be obtained in a simpler way by the 
following process. Place in a flask three parts of com- 
mon salt and five parlsof sulphuric acid, (oil of vitriol.) 
As the acid is rapidly generated, it may be conducted 
by a bent tube into a vessel containing three parts of 
water, this will absorb the gas and form a solution of 
hydrochloric acid, which is the muriatic acid of com- 
merce. 

The gas when pure, is transparent and colorless ; 
heavier than atmospheric air in nearly the ratio of 13 
to 10. With regard to its influence when applied to 
soils, Johnston uses the following language. 

" When applied to living vegetables in the state of an 
exceedingly dilute solution in water, it has been suppo- 
sed upon some soils, and in some circumstances, to be 
favorable to vegetation. Long experience, however, 
on the banks of the Tyne, and elsewhere, in the neigh- 

What other name for muriatic acid 1 Is formed by the combination 
of what elements % How are they made to combine 1 What is the 
equivalent of this acid 1 Is it a liquid or a gas ? How is the liquid hy- 
drochloric acid obtained? Describe the process for manufacturing the 
muriatic acid of commerce ? 



52 AGRICULTURAL CHEMISTRY. 

borhood of the so called alkali works, has proved that 
in the state of vapor its repeated application, even when 
diluted with much air, is often fatal to vegetable life. 

Poured in a liquid state upon fallow land, or land 
preparing for a crop, it may assist the growth of the 
future grain, by previously forming, with the ingredients 
of the soil, some of those compounds which have been 
occasionally applied as manures." 

HYDROFLUORIC ACID. 

HF=19. 

When speaking of fluorine, it was stated that this ele- 
ment had never been obtained in its uncombined state. 
The simplest form in which it has been obtained, is 
that of its combination with hydrogen, forming hydroflu- 
oric acid. This compound is derived from a mineral called 
fluor spar. When this is pulverized and distilled in a lead- 
en vessel with twice its weight of oil of vitriol, a colorless 
liquid heavier than water is obtained, very corrosive, 
and possessing the remarkable property of acting upon 
glass. This property is best illustrated by coating a piece 
of glass with a film of bees wax, and writing or sketching 
some picture in the coating. This is to be laid over a 
flat leaden vessel containing the mixture of fluor spar and 
sulphuric acid. Wherever the wax has been removed, 
the glass will be deeply etched. Hydrofluoric acid has 
recently been detected in the ashes of plants. 

PROTOXIDE OF POTASSIUM, POTASSA, OR POTASH. 

K 0=48. 

When the metal potassium is thrown upon water, 
decomposition ensues ; the metal burns with a beautiful 

What is said of the influence of this acid upon vegetation ? From 
what is hydrofluoric acid obtained ] Give the process. What remarkable 
property does this acid possess ? How may glass be etched by it ? 



PROTOXIDE OF POTASSIUM, POTASSA, OR POTASH. 53 

pink flame. The oxygen of the water unites rapidly 
with the metal forming protoxide of potassium, and the 
heat produced by the combination sets fire to the hy- 
drogen evolved. The compound formed is commonly 
called potash ; at the close of the experiment the fused 
globule of potash unites explosively with the water. It 
is very difficult to obtain potash perfectly free from wa- 
ter, but when in this state it is said to be anhydrous^ 
(destitute of water.) When combined with water it is 
said to be hydrated^ (containing water,) and the chemi- 
cal name of potash in this state, is hydrated oxide of 
potassium. Potash may be obtained by the following 
process. Dissol ve one part pearl ashes, or better, sal tar- 
tar in twelve parts of water : boil the solution and add 
while boiling one part of slacked lime, made into a 
cream with hot water ; this should be added by degrees. 
The air should be excluded from the vessel by means 
ofa tight lid, while the contents are cooling. After 
the lime has settled, the clear liquid is drawn off by 
means ofa syphon, and this must be evaporated until 
it will consolidate in cooling ; the potash in this state 
may be cast into the form of cylinders — the form of the 
caustic potash of the shops. Potassa in this form is a 
white solid, but absorbs moisture from the air and soon 
becomes liquid, unless kept in well stopped bottles. It 
acts energetically upon animal and vegetable substan- 
ces, decomposing and dissolving them. Potash is an 
alkaliy neutralizing the strongest acids, restoring the 
colors that have been changed to red by an acid, and 
changing some vegetable colors to green- — as infusion 
of red cabbage. Since the potash of commerce is de- 
rived from the ashes of plants, it follows that it must be 

What is the chemical equivalent of potassa 1 What compound is 
formed by throwing potassium upon water ] What term is applied to po- 
tassa when free from water? When it contains water what is it called? 
Give the process for obtaining potash. What are the properties of pot- 
ash ? From wliat source is the potash of commerce derived ? 

E* 



54 AGRICULTURAL CHEMISTRY. 

a constituent of plants and of the soils upon which they 
grow, and without doubt acts an important part in vege- 
tation. Potash does not occur in nature, however in 
its caustic stale, but in combination with carbonic acid, 
&c., forming compounds of which we shall speak here- 
after. Caustic potash is supposed to be formed, in 
small quantity, in compost heaps, from the compounds 
of potash contained therein, and by its decomposing 
power to render the vegetable matter soluble ; fitting it 
for supplying nourishment to the plant* 

PROTOXIDE OF SODIUM, OR SODAs 

NaO=32. 

The metal sodium when thrown upon water, decom- 
poses it rapidly, and if prevented from moving about 
upon the water, will take fire, like potassium. Hydra- 
ted protoxide of sodium or caustic soda is the result. 
Soda may be obtained from the commercial carbonate 
of soda by the same process as that given for caustic 
potash, and closely resembles the latter in all its proper- 
ties. It is a constituent of soils and plants, but always 
occurs in a state of combination. Common salt in com- 
post heaps is sometimes converted into caustic soda, 
and in this form prepares the vegetable matter to be 
taken up by the plant. Soda is an alkali. 

CHLORIDE OF SODIUM, OR COMMON SALT. 

ClNa=60. 

Common salt, so familiar to all, exists very abundant- 
ly in nature, in the waters of the sea, and in the mineral 

Is it a constituent of plants and soils 1 Give the composition and 
equivalent number of soda. How may caustic soda be procured ? Its 
properties? From what is it sometimes formed in compost heaps? 
Where is common salt found ? 



DHLOEIDE OF SODIUM, OR COMMON SALT. 55 

crust of the earth, forming deposits of rock salt, and in 
saline springs which probably obtain their salt from 
such deposits. It is a compound of the gas chlorine 
with the metal sodium ; most of its properties are known 
to all. It may be detected in the ashes of all plants, 
and in nearly all soils. "It is well known that common 
salt has been employed in all ages and all countries for 
the purpose of promoting vegetation, and in no country 
perhaps, in larger quantities than in England. That it 
has often failed to benefit the land in particular locali- 
ties, only shows that the soil in those places already 
contained a natural supply of this compound large 
enough to meet the wants of the crops which grew 
upon it." — (Johnston.) Salt has been highly recom- 
mended by some and denounced by others, and men 
are more likely to remember a failure than a successful 
experiment. But a few months since a report was 
given by the committee on agriculture of the New 
York Legislature, in which some statements were 
made, showing the effects of salt as a manure. This 
induced some farmers to try the virtue of it upon their 
own soils. Some were disappointed, and probably 
concluded that it is useless as a fertilizer, but in 
hazarding such experiments it must be remembered 
that a difference of soil is sufficient to account for all 
such failures. If the character of the soil upon which 
salt has acted favorably, is definitely known, and the 
crop which was benefited by its action be known also, 
there can scarcely be a chance of failure in applying 
salt to the same crop on a similar soil. 

Has it ever been employed as a fertilizer ? With what success ? Why 
has it failed in particular localities ? 



56 AGRICULTURAL CHEMISTRY. 

PROTOXIDE OF CALCIUM, OR LIME« 

Ca 0=28. 

If the metal calcium be thrown into water, it 
decomposes this hquid as do potassium and sodium ; ta- 
king up the oxygen and liberating hydrogen ; the 
compound formed is the protoxide of calcium. If this 
combination is produced without the presence of water 
there is formed a white substance, known as quickhme 
or Hme. If water be present, a hydrate of lime is 
formed, (slacked lime) containing about |^ of its weight 
of this liquid. Quicklime is usually obtained for agri- 
cultural and other purposes, from the common lime- 
stone that forms so great a share of the rock formations 
of the earth's surface. This rock is subjected to an in- 
tense heat, until it loses about 44per cenl. of its weight, 
leaving nearly pure lime. 

The union of water with lime, produces a great de- 
gree of heat— sufficient to fire wood, and inflame gun- 
powder. Lime is slightly soluble in water, and its solu- 
tion is somewhat caustic and alkaline. It occurs exten- 
sively diffused, forming a share, and in many cases a 
large share of the different soils, and a large part of 
some mineral masses. It also occurs m the ashes of 
plants, and in the bones of animals, but in none of these 
positions does it occur in an uncombined form. Lime 
is frequently applied to soils, and with marked effect. 

It not only exerts a beneficial influence in vegetation 
by supplying food to the plant directly from its own 
substance, but it seems to have the power of working 

What is the chemical name of lime 1 What is its composition ? 
When combined with water what is formed? Whence is quicklime 
usually obtained 1 Mention its properties. Where does it occur ? In 
what manner does lime act favorably upon vegetation ? What is its 
effect upon different soils ? 



PROTOXIDE OF CALCIUM, OR LIME. 67 

changes in other compounds, and thus prepares them 
for becoming nourishment for the plant. By mixture 
with soils of a stiff clayey nature, it renders them po- 
rous and thus mechanically improves them. Upon soils 
of a light sandy nature however, the same effect only 
renders them more unproductive, yet lime may be 
applied to light soils with good effect, if accompanied 
by other substances. In connection with vegetable 
matter in almost any form it renders such soils fertile, 
but should never be applied to them unmixed with veg- 
etable manures — the reason will be given hereafter. 
The question naturally arises, "In what forni should 
lime be applied, in that of hydrate, or should it be un- 
slacked?" If it be the object of the agriculturalist to 
extirpate useless weeds and grasses, or to decompose 
rapidly the different kinds of vegetable matter in the 
soil, it should be applied fresh from the kiln in its 
caustic, unslacked state. But when it isapplied for the 
purpose of stimulating the growth of tender herbage, it 
should first be permitted to slack spontaneously, lest it 
act too energetically upon the young plant. In many 
cases it is immaterial in what form it may be applied. 
Lime should be applied, generally, sometime before the 
crop to be benefited is sown. If clover is to be plough- 
ed in, or green sward to be broken up, it is better to 
apply the lime upon the surface before ploughing. To 
explain the various changes produced by lime, it will be 
necessary to treat of many compounds not yet described, 
we therefore omit the farther consideration of the sub- 
ject in this connection. 

With what should it be mixed before it is applied to light soils 1 
When should it be applied in its unslacked form 1 When should the 
hydrate be applied ? In what cases should it be applied before plough- 
ing? 



58 AGRICULTURAL CHEMISTRYe 

CHLORIDE OF CALCIUM. 

Ca Cl=56. 

This compound of chlorine and calcium, may be 
formed by dissolving chalk in hydrochloric (muriatic) 
acid, and evaporating the solution until it will crys- 
talize in cooling. In this state it has two proportions 
of water, — called water of crystalization. It may be 
rendered anhydrous by exposing it to a red heat. In 
this form it is a white solid, phosphorescent in the dark, 
and having so great an affinity for water, that if ex- 
posed to the air, it rapidly absorbs moisture and chang- 
es to the liquid form. Compounds that possess this 
property of absorbing water and becoming liquid, are 
said to be deliquescent. Not only are the elements of 
this compound found in plants, but chloride of calcium 
itself has been detected in the sap. It would seem then 
that if it could be easily obtained, it might be very benefi- 
cially applied to the plant. With regard to the sources 
from which it may be obtained, and the effect of its 
application, Johnston makes the following statements. 

" In reference to the culture of potatoes, I will here 
bring under your notice the chloride of calcium, which 
is said to have been beneficially applied to various 
crops, to potatoes especially, with surprising effect. Un- 
der the influence of this substance, the sunflower and 
maize have grown to the height of 14 to 18 feet, and 
potatoes have attained the weight of 2 to 3 pounds. 
This compound occurs in sea water, and is also contain- 
ed largely, though mixed with other substances, in the 
mother liquor of the salt pans, and from the numerous 
salt works of the coast, might readily be obtained for 
trial." 

How is chloride of calcium formed 1 What is said of its avidity for 
moisture ? What term is applied to those compounds that become liquid 
by absorbing moisture I 



JPROTOXIDE OF MAGNESIUM, OR MAGNESIA. 59 



FLUORIDE OF CALCIUM, OR FLUOR SPAR, 

CaF=38. 

Fluor Spar, the mineral from which hydrofluoric acid 
is obtained, (see page 52) is a compound of fluorine and 
calcium. The same compound is found in small quan- 
tity in the bones of animals, and since the substance of 
all animal forms must have been derived from their food, 
it seems a necessary inference that plants must contain 
this compound. It has been detected in the ashes of 
plants, in minute quantity, but probably does not exert 
a very important influence upon vegetation. 

PROTOXIDE OF MAGNESIUM, OR MAGNESIA. 

Mg 0=20 

Magnesium heated to redness in the open air burns 
brilliantly, and forms magnesia or the protoxide of mag- 
nesium ; this is identical with the calcined magnesia of 
commerce. It is similar to lime in many of its proper- 
ties and is sometimes found in limestones ; such receive 
the name of magnesian limestones. The quicklime ob- 
tained from such rocks, when applied to land sometimes 
produces injurious effects, probably from the quantity 
employed. It has been suggested that it is owing to the 
compounds formed by the union of magnesia with nox- 
ious acids which exist in the soils. In this way salts 
are formed which are quite soluble in water, and are 
carried into the circulation of the plant. 

It should be borne in mind, however, that this com- 

What is said of the effect of fluoride of calcium upon vegetation! 
Give the chemical composition of fluor spar. Where is this compound 
found ? Whence must it have been originally derived 1 Why is the 
combining number of magnesia 20 ? What is the effect of quicklime 
containing magnesia upon plants ? 



60 AGRICULTURAL CHEMISTRY, 

pound is a very essential ingredient of most plants, and 
therefore substances containing it in limited quantity, 
should be supplied to the soil. 

OXIDES OF IRON. 

Protoxide, Fe 0=36. Peroxide, Fez O3=80o 

When iron is exposed to air and moisture, the sur- 
face becomes covered v^ith a reddish brown sub- 
stance, which is called rust ; this is the peroxide of iron. 
It occurs very abundantly in soils, giving to them 
their red color. It not only supplies food to the plant 
from its own substance, but seems to have the power of 
absorbing ammonia, and retaining it as nourishment for 
the plant. If in connection with this oxide, there is a 
large quantity of vegetable matter in process of de- 
composition, the peroxide becomes changed to a protox- 
ide, a part of the oxygen uniting with the carbon, to form 
carbonic acid. The protoxide readily combines with 
certain substances, and the compounds formed are 
mostly soluble in water, and in this way pass into the 
circulation of the plant, proving, in some cases, exceed- 
ingly injurious. If the soil, however, in which these 
noxious compounds occur be kept loose and porous, they 
will be decomposed by the action of the atmosphere and 
the protoxide again become a peroxide. Soils then 
which contain much oxide of iron, should be frequently 
broken up and exposed to the oxydizing action of the 
atmosphere. 

Is magnesia a necessary element in vegetation ? What oxide is found 
by exposing iron to air and moisture ? Where does this oxide occur? 
What property does it possess by which it facilitates the growth of the 
plant ? How is it converted into protoxide 1 In this form is it preju- 
dicial to the plant. How may the protoxide in the soil be converted 
into a peroxide 1 



OXIDES OF ALUMINUM, OR ALUMINA. 61 



OXIDES OF MANGANESE. 

Protoxide, Mn 0=36. Deutoxide, Mn2 03=80. 
Peroxide, Mn 02=44. 

The substance known as the black oxide of mangan- 
ese is a compound of manganese and oxygen in the pro- 
portion of one atom of the former to two of the latter, 
and its equivalent number is 44, as given above. This 
compound is called the peroxide, and occurs abundantly 
in nature, very frequently combined with the various 
ores of iron. When exposed to heat, as in the experiment 
for obtaining oxygen, (page 21,) it abandons a portion 
of its oxygen and is changed to the deutoxide, Mna Os 
=80. This compound also occurs in considerable 
quantity in nature, and resembles the peroxide in ap- 
pearance. If the latter be heated to redness in a glass 
tube, and a stream of hydrogen be made to pass through 
it, the protoxide of manganese will be formed, a green- 
ish gray substance. These oxides are insoluble in wa- 
ter, and therefore can not enter into the circulation of 
the plant without first forming soluble compounds with 
other substances contained in the soil. 

OXIDE OF ALUMINUM, OR ALUMINA. 

AI2 03=52. 

The metal aluminum slowly decomposes boiling wa- 
ter, uniting with its oxygen to form alumina, and evolv- 
ing the hydrogen. Pure alumina is a white solid, taste- 
less, and insoluble in water. Though it forms but a small 

What is the chemical constitution of the peroxide of manganese ? To 
what is it changed in the process for obtaining oxygen ? How is the 
protoxide of manganese obtained 1 Why do not these oxides enter di- 
rectly into the circulation of the plant? What is the effect of aluminum 
upon boiling water 1 What are the properties of alumina ? 



62 AGRICULTtJRAL CHEMISTRY. 

proportion of the plant, it seems to act indirectly in fa- 
cilitating the growth of vegetable forms. This com- 
pound is the principal ingredient in all clays. Burned 
clay when applied to soils has proved very beneficiaL 
This effect is undoubtedly due to the property of ab- 
sorbing ammonia which alumina possesses. That clay 
retains ammonia may be shown by moistening it with 
a solution of caustic potash, or by mixing quicklime 
w^ith it and moistening the mixture ; in either case am- 
monia will be evolved, and may be made apparent by 
holding over the mixture a feather dipped in vinegar 
or muriatic acid, when white fumes will be formed by 
the union of the ammonia and acid. 

Nearly pure alumina may be obtained from alum by 
dissolving in water, and addinga solution of pearlash as 
long as a white precipitate is produced. This white 
substance must be separated by filtering, washed and 
dried. This substance is found nearly pure in some of 
the rarer minerals, and impure in the slates and shales 
of the crust of the earth ; it is an ingredient in most soils, 
giving them tenacity and rendering them retentive of 
moisture. If it exists in too great proportion, it renders 
a soil cold and wet from its being impervious to water. 

The primary compounds have now been treated of 
separately, but it will be noticed that some of them are 
not found in soils or plants uncombined. It will be neces- 
sary therefore, to treat of the secondary compounds 
formed by the union of the primary with each other. 
The different elements of the plant are for the most 
part derived from these compounds. 

It is the principal ingredient of what 1 To what is the favorable ac- 
tion of burned clay upon vegetation owing 1 How may it be shown that 
clay retains ammonia ? How may alumina be obtained in a nearly pure 
form 1 What is the effect of alumina upon soils ? Do the primary com- 
pounds generally occur in the soil uncombined with each other ? 



PART III 

SECONDARY COMPOUNDS. 



NAMES. 



By examining the table of primary compounds (page 
34,) it will be seen that nearly all the acids given, are 
formed by the union of oxygen with the non-metallic 
elements. The combination of oxygen with the metal- 
lic elements, generally in one proportion, forms a class 
of compounds called bases. Oxygen in some cases, 
unites with a metal in one proportion forming a hase^ 
and in other proportions forming an acid, or perhaps 
more acids than one. Thus we have the protoxide of 
manganese as a base, but manganese uniting with three 
proportions of oxygen forms manganic acid. Potassa, 
soda, lime, protoxide of iron, protoxide of manganese, 
&c., are bases. Acids combine with bases to form a 
class of secondary compounds called salts. Ammonia, 
formed by the union of two non-metallic elements, is 
also a base, and forms salts by combination with the 
different acids. 

In examining the secondary compounds, we shall take 
up the first base in the list, and consider its combinations 
with the several acids. 

We give below a list of these compounds, beginning 
with ammonia as a base. The following rules are ob- 
served in giving names to these compounds. If the 
name of the acid ends in ic, that termination is changed 

How are most of the acids formed 1 How are bases formed ? What 
do the combination of acids and bases produce ? 



64 AGRICULTURAL CHEMISTRY. 

to ate, and the word thus changed, united with the name 
of the base, forms the name of the compound. Nitric 
acid unitinf^ with soda forms a mirate of soda, sulphuric 
acid with the same base, a sulphate of soda. If the 
acid ends in ous, that termination is changed to ite in 
giving the name of the salt. Thus, sulphurous acid 
forms sulphides of the several bases. 

In the column of symbols it will be noticed that the 
salts of ammonia are not represented by the combina- 
tion of the symbols of the acid and base, as we might at 
first expect, for instance, we have for nitrate of ammo- 
nia, N O 5 +N H4 O instead of N O5 +N Hs. There 
is a hypothetical compound of a metallic nature, called 
ammonium, containing one proportion of hydrogen 
more than ammonia contains, and its symbol is N H4 or 
merely Am. It has been produced in connection with 
other metals, but has never been separated from them : 
it is therefore called a hypothetical compound. In the 
formation of the nitrate, sulphate, and carbonate of am- 
monia, this metal in the form of an oxide unites with 
the several acids. 

According to this view, the base ammonia like other 
bases, is formed by the union of oxygen with a metal. 

The symbols and equivalents of certain compounds 
are omitted, because it would be unprofitable here to go 
into an explanation of them. The compound called 
muriate of ammonia is perhaps strictly speaking, a chlo- 
ride of ammonium, and its symbol CI N H4 or CI Am, 
but the elements combined are the same whether it be 
considered one way or the other. 

Certain of the salts contain a portion of water called 
water of crystalization ; thus, the sulphate of iron in its 

When the name of the acid ends in ic, how is the name of the salt 
formed ? How when the acid ends in ous ? W^hat is the constitution 
of ammonium ] In what form does this metal unite with the acids ? 
What IS said of muriate of ammonia? 



k 



NAMES. 



65 



cryslalized form contains seven proportions of water, its 
symbol therefore, would be S Os+Fe 0+7 Aq, (Aq 
signifying water,) and its equivalent 139. The symbol 
given in the table will apply only to the sulphate after 
it has been deprived of its water by heat. In the sym- 
bols of several other compounds, the water which they 
usually contain is not indicated. 

Table of Secondary Compounds. 



1 Names. 


Common Names. 


Symbols. 


Equiv. 


Nitrate of Ammonia, 




NO5+NH4O 


80 


Carbonate " 




CO2 + NH4O 


48 


Sulphate 




SO3+NH4O 


66 


Phosphate 








Muriate " 


Sal Ammoniac, 


HCI + NIIa 


54 


Nitrate of Potassa, 


Nitre, Saltpetre, 


NO5+KO 


102 


Carbonate 


Sal tartar, Pearlash 


CO2+KO 


70 


Silicate 








Sulphate 




SO3 + KO 


88 


Nitrate of Soda, 




NOs+NaO 


86 


Carbonate " 




C02+NaO 


54 


Silicate 








Sulphate " 


Glauber's Salt, 


S03+NaO 


72 


Nitrate of Lime, 




NOs+CaO 


82 


Carbonate " 


Chalk, Limestone, 


COs+CaO 


50 


Silicate " 








Sulphate " 


Gypsum, Plaster, 


SOa+CaO 


68 


Phosphate " 








Nitrate of Magnesia, 




NOs+MgO 


74 


Carbonate " 




COa + MgO 


42 


Silicate 








Sulphate " 


Epsom Salts, 


SOs + MgO 


60 


Sulphate of Iron, 


Copperas, 


SOs+FeO 


76 


Carbonate " 




C02+FeO 


58 


Sulphate of Manganese, 




SOs + MnO 


76 


Silicate of Alumina, 









How many proportions of water does the sulphate of iron contain ? 
To what does its symbol given in the table apply 1 



66 AGRICULTURAL CHEMISTRY. 

NITRATE OF AMMONIA. 

NO5-|-NH4O==:80. 

Ammonia added to nitric acid neutralizes its acid pro- 
perties, and by evsiporaiion 3. deliquescent salt is obtained, 
called the nitrate of ammonia. We have mentioned be- 
fore the formation of nitric acid during thunder showers ; 
this acid so formed, unites with the ammonia that is ever 
present in the atmosphere, and forms nitrate of ammonia. 

We may here state that it is supposed by some, and 
with reason, that in the formation of nitric acid under 
the circumstances mentioned, the nitrogen is derived 
from ammonia, rather than from the constituents of the 
atmosphere. When the nitrate is brought to the earth 
it is soon decomposed, the nitric acid forms other ni- 
trates in the soil, of which we shall speak hereafter, and 
the ammonia is set free, passing into the atmosphere or 
perhaps in part into the circulation of the plant. The 
nitric acid is thus retained in the soil, and acts bene- 
ficially upon the plant. 

An instance of the effect of nitrate of ammonia as a 
manure is given by Petzholdt. A meadow which with- 
out manure produced 8,000 lbs. of hay, after the ap- 
plication of this salt, yielded 1 1,200. 

CARBONATE OF AMMONIA, OR VOLATILE SALTS. 

C02+NH4 0=48. 

If we arrange a flask containing the materials neces- 
sary for generating ammonia, (see page 39) and another 
supplied with the substances used tor producing car- 
bonic acid, (page 42) and cause the gases to be convey- 



I 



How is nitrate of ammonia formed ? How is it formed in nature ? 
Will nitrate of ammonia remain fixed in the soil? What instance is 
given of the nitrate of ammonia as a manure 1 How may the carbonate 
of ammonia be formed ? What is the common name of this compound ? 



CARBONATE OF AMMONIA, OR VOLATILE SALTS. 6? 

ed into the same receiver, an incrustation of carbonate 
of ammonia will be formed upon the receiving vessel. 
This salt has the pungent odor of ammonia, but it is 
not the common sal volatile of commerce ; this com- 
pound is usually obtained by exposing a mixture of 
powdered chalk and sal ammoniac to a high heat in an 
earthern retort. The salt forms a crust upon the inside 
of the receiver. This form of the carbonate is not a 
simple salt, but a mixture of two, because by washing 
with water or alcohol we have remaining the bi-carhon- 
ate of ammonia (the prefix bi signifying that they are 
two proportions of carbonic acid,) and that which is 
washed out is the carbonate. There are other salts 
formed by the union of carbonic acid with ammonia, 
but in treating of their influence upon vegetation, we 
shall use the term carbonate of ammonia merely, with- 
out reference to the more complex compounds. 

We have before spoken of the sources from which 
the gas ammonia is supplied to the air and of the favor- 
able influence it exerts upon vegetation. When it is 
given off" from the soil, the compost heap, or from de- 
caying substances, it generally unites immedtately with 
carbonic acid, these gases being often generated simul- 
taneously in the decomposition of different substances ; 
but when ammonia does not unite with this acid imme- 
diately, it passes into the atmosphere, and coming in 
contact with the carbonic acid of the air, unites with it. 
The carbonate thus formed is brought down in greater 
or less quantity, by every shower. We have seen be- 
fore that, under certain circumstances, nitrate of ammo- 
nia will be formed, but nitric acid is not usually con- 
tained in the atmosphere, whilst carbonic acid is a con- 
stant constituent. It follows then, that ammonia will 
be usually converted into a carbonate. 

How is it usually obtained ] How may it be shown that the common 
form of the carbonate consists of two sails ] What is the signification of 
fei-carbonate 1 With what does ammonia usually combine as it is formed ? 



68 AGRICULTURAL CHEMISTRY. 

The carbonate of ammonia, by decomposing com- 
pounds contained in the soil or compost heap, often ex- 
erts a more beneficial influence upon vegetation than 
ammonia uncombined with an acid. It decomposes 
gypsum or plaster, as will be shown hereafter when 
treating of that compound. Ammonia, it will be recol- 
lected, is a compound of hydrogen and nitrogen, and 
from this compound the plant probably obtains both of 
these elements; but hydrogen may be supplied from 
other sources, whilst the agriculturalist must depend 
almost wholly upon ammonia or its compounds for a 
supply of nitrogen ; and since ammonia either un- 
combined or in the form of a carbonate is volatile, and 
will not remain fixed in the soil, it is of the first impor- 
tance that we should ascertain some method by which 
it may be retained, so that its nitrogen may be assimmi- 
lated by the plant. There are certain compounds, soon 
to be examined, that are chiefly beneficial on account of 
their power o^ fixing in the soil the volatile ammonia of 
the atmosphere. 

SULPHATE OF AMMONIA. 

SOa-fN H40=6G. 

If the acid properties of oil of vitriol be neutralized 
by adding carbonate of ammonia, the acid, by its com- 
bination with ammonia forms a salt, and carbonic acid 
is set free. The compound formed is the sulphate of 
ammonia. It crystalizes, holding in combination one 
proportion of water, and is never obtained free from it. 
The proper symbol then for it is S Os+N H4 0+Aq. 

Sulphate of ammonia is a valuable fertilizer, since it 

In what way does carbonate of ammonia exert a favorable influence 
upon vegetation 1 What does ammonia supply to the plant ? Will am- 
monia, either uncombined or in the form of carbonate, remain fixed in 
the soil ] Of what is sulphate of ammonia formed 1 



PHOSPHATE OF AMMONIA. 69 

supplies two important substances to the plant, ammo- 
nia and sulphuric acid, yet, this salt can seldom be ap- 
plied economically to the soil. It may be formed 
however by the agriculturalist by neutralizing the am- 
monia which is contained in liquid manures, by means 
of oil of vitriol, and thus this volatile gas is retained in 
a form suited to the wants of the plant. If the hquid 
excrements of men and animals be preserved and neu- 
tralized by sulphuric acid, the sulphate of ammonia 
produced, will form, with the other compounds con- 
tained by such fluids, an exceedingly rich manure. 

The following statement by Petzholdt shows the 
value of this ammoniacal salt as a fertilizer. 

" From a meadow which had not been manured 8000 
lbs. of hay were obtained, after the use of sulphate of 
ammonia as manure, the same surface yielded 10,466 
lbs,, being 2, 466 more." 

PHOSPHATE OF AMMONIA. 

This compound of phosphoric acid and ammonia is 
detected in human urine and guano, and is a very im- 
portant constituent of such manures. It will be seen 
hereafter that the ashes of the grains of w^heat contain 
nearly fifty per cent, of phosphoric acid, rye about forty- 
seven, &c. The effect then of phosphate of ammonia 
upon vegetation might be inferred without recourse to 
experiment ; and the same is true of other phosphates. 
The richest manures owe their fertilizing qualities to 
the presence of compounds of phosphoric acid with am- 
monia, lime, soda, magnesia, &c. 

What does sulphate of ammonia supply to the plant? How may sul- 
phate of ammonia be formed by the agriculturist ? Give an instance of 
the effect of this compound as a manure] What important compound 
is contained by guano, &c.? How extensively does it occur in the grains 
of wheat and rye ? What is said of the fertilizing qualities of the rich- 
est manures 1 



70 AGRICULTURAL CHEMISTRY. 

MURIATE OF AMMONIA, OR SAL AMMONIAC. 

HCI+NH3=54. 

Sal ammoniac, a compound known to all, is formed 
whenever ammonia and muriatic acid gas are permitted 
to mingle. If the two gases be passed into a receiver, 
they will combine and form pure muriate of ammonia 
in the form of snow white powder. The commercial 
sal ammoniac is formed by neutralizing ammoniacal 
liquors, obtained by the destructive distillation of horns 
and bones, with common muriate acid, and evapora- 
ting until the liquid will crystalize in cooling. The 
more scientific name of this compound is hydrochlorate 
of ammonia, since the proper name of the acid is hydro- 
chloric, and not muriatic. Its action as a fertilizer is 
like that of the sulphate of ammonia, but perhaps more 
marked, and the agriculturalist can form the compound 
by saturating the liquid manures containing ammonia, 
with muriatic acid. By this means the ammonia is ren- 
dered non-volatile, aud will not escape into the atmos- 
phere after being applied to the soil. It is stated by 
Petzholdt that a meadow which without manure pro- 
duced 8,000 pounds of hay, after the application of hy- 
drochlorate of ammonia yielded 11,432 pounds, an in- 
crease of 3,432 pounds. 

A solution of muriate of ammonia is sometimes used 
for soaking seeds before they are deposited in the 
ground ; when thus treated the seed is said to sprout 
sooner, and the young plant to grow more vigorously. 

How is muriate of ammonia formed 1 What are the different names 
for this compound? Give the statement of Petzholdt? What is the ef- 
fect of sal ammoniac upon seeds ? 



NITRATE OF POTASH, SALTPETRE, OR NITRE. 71 

NITRATE OF POTASH, SALTPETRE, OR NITRE. 

NCs+K 0=102. 

Nitre may be formed by uniting nitric acid with pot- 
ash, or its carbonate and evaporating until it crystal- 
lizes. The nitre of commerce is derived mostly from 
certain soils, called salt petre grounds, in which either 
the nitre is found ready formed, and can be obtained by 
merely lixiviating the soil, or nitrate of lime is contained, 
which can be easily decomposed by carbonate of potash 
so as to form the nitrate. The soils in which nitre oc- 
curs generally contain animal and vegetable matter, and 
artificial nitre beds may be formed by mixing animal 
and vegetable substances with lime, ashes and earth. 
It is a question whether the elements of the atmosphere 
are made to combine by electrical agencies, to form 
the nitric acid of the nitrates in the soil, or whether the 
nitrogen arising from the decomposition of animal and 
vegetable substances unites with the oxygen of the air 
to form the same. 

Nitre is found in certain plants, and in the dried stems 
of some vegetable forms, even occurs in needle-form 
crystals. It is evident that this salt will act favorably 
upon such plants, and experiment has shown that when 
applied to the soil in proper quantity, it greatly pro- 
motes the growth and luxuriance of all crops. If pre- 
sent in the earth in excess, it is hostile to vegetable life, 
and renders the soil barren. The earth obtained from 
localities in which this compound accumulates ; as the 
ruins of old buildings, the earth of cellars, stables and 
certain caves ; may be profitably mixed with other ma- 
nures to form valuable composts. 

From what source is the nitre of commerce derived ? How is it ob- 
tained 1 How may artificial nitre beds be formed ? What is said of the 
existence of nitre in plants 1 What effect has nitre when applied to the 
soil] What the effect of large quantities? What is said of the earth, 
of cellars, stables, &.c. 1 



72 AGRICULTURAL CHEMISTRY. 

CARBONATE OF POTASH, OR SALT OF TARTAR. 

CO2+KO=70. 

Impure carbonate of potash may be procured by lix- 
iviating wood ashes, and evaporating the liquid thus 
obtained. If this be dissolved in v^rater, and the clear 
fluid drav^^n off and evaporated, another form of the car- 
bonate is obtained called pearlash, but this form, too, is 
impure. Pure carbonate of potash is obtained by cal- 
cining cream of tartar, dissolving out the salt by means 
of water, and evaporating the liquid to dryness. This 
form is called salt of tartar. It is hardly necessary to 
say that carbonate of potash, in any form, exerts a pow- 
erful influence upon vegetation. Wood ashes have been 
employed for the purpose of increasing the fertility of 
the soil, in almost every country and from the earliest 
times, and their favorable action depends mostly upon 
the carbonate of potash contained. The action of this 
compound is much more favorable upon some crops 
than others, because it is contained in greater quantity 
by certain plants than by others. 

When the importance of potash is considered — it 
being a necessary constituent of every fertile soil — it 
becomes a matter of surprise that the farmer should dis- 
pose of the ashes which he obtains by burning wood, 
at a price really far below their real worth ; their value, 
however, does not depend merely upon the amount of 
potash contained, for besides this compound there may 
be found soda, lime, magnesia, silica, alumina, oxides of 
iron and manganese, sulphuric acid, phosphoric acid, 
&c. Wood ashes, even after they have been lixiviated 



What is the chemical name of salt of tartar 1 How are the different 
forms of carbonate of potash obtained X What is said of the effect of the 
carbonate upon vegetation? Of the value of wood ashes? Are ashes 
valuable which have been deprived of their potash ? Why ? 



SILICATE OF POTASH. 73 

and thus deprived of their potash, still contain many 
valuable ingredients, and may be advantageously ap- 
plied to soils. 

Ashes seem to have the power, not only of facilitating 
the growth of useful plants, but also of exterminating 
useless ones, for when applied to coarse grasses they 
disappear, and more tender and nutritious ones supply 
their place. 

SILICATE OF POTASH. 

Silica combines with potash in different proportions, 
forming silicates, but it is difficult to discover their ex- 
act chemical constitution, and therefore the symbol 
and chemical equivalent of the compound under con- 
sideration, are omitted. 

The principal ingredients of glass are silica, potash, 
soda, and lime ; when these are fused together, the 
silica unites with the others forming silicates. Potash 
and silica fused together, form a kind of glass, and if a 
considerable proportion of potash be used the compound 
will be soluble in water. This composition is called 
liquor of flints. Glass formed by fusing together 76 
parts of fine white sand, 27 of dry carbonate of soda, 
and 35 of carbonate of potash, is soluble in water, and 
when the solution is applied to wood it is said to render 
it incombustible. 

Silica in its uncombined form, it will be recollected, 
is insoluble in water ; we infer therefore that it can not 
be assimilated by the plant, unless it be first combined 
with some substances to form soluble compounds. Pot- 
ash and soda are the substances with which it usually 
unites. The insoluble silicates may be decomposed by 

What is the effect of wood ashes upon coarse grasses ? What is sili- 
cate of potash ? What are the ingredients of glass] Soluble glass? 
Is silica soluble in water ? What change must take place before it can 
be taken up by the plant 1 With what substances does it usually unite t 



74 AGRICULTURAL OHEMISTRYe 

the carbonic acid of the air ; indeed, this process ol de- 
composition is continually going on wherever the siUc- 
ates exist in the soil or in rocks, and the silica which is 
separated is slightly soluble in water, and considerably 
so in solutions of potash, soda, &c. We see then the 
importance of supplying silicates, either soluble or inso- 
luble, to those soils which are destitute of them, or at 
least of supplying a sufficient quantity of potash to unite 
with the silica in the soil, and thus provide for the w^ants 
of the plant. 

Wood ashes contain a certain portion of the silicates,, 
and hence their favorable action upon plants that require 
much silica. Plants may be so classified as to indicate 
the compound predominent among their constituents. 
They are sometimes divided into three classes, silica 
plants, lime plants, and potash plants. Oats, barley,. 
hay, &c. are silica plants, their ashes containing a large 
percentage of silica. 

SULPHATE OF POTASH. 

S03+KO=88. 

This salt may be formed by the combination of sul- 
phuric acid and potash, but the sulphate of commerce 
is produced by the decomposition of nitrate of potash 
by oil of vitriol in the manufacture of nitric acid. Sul- 
phate of potash is a crystaline salt, and sparingly solu- 
ble in cold water. It exerts a favorable influence upon 
vegetation when supplied to the soil, but can not be 
economically applied in its pure form as a manure, on 
account of its high price. It occurs, however, in the 
ashes of wood, and in this form may be applied, in con- 
How are the insoluble silicates decomposed? What should be sup- 
plied to soils ] How may sulphate of potash be formed ] What is the 
effect of sulphate of potash upon vegetation ? Where is it found in con- 
nection with other substances- ] 



i 



* 

NITRATE OF SODA. 75 

nection with other substances. Its favorable action 
seems to depend upon the supply of sulphur and potash 
to the plant. 

" Dissolved in 100 times its weight of water, the sul- 
phate of potash has been found to act favorably on red 
clover, vetches, beans, peas, &c., and part of the effect 
of wood ashes on plants of this kind is to be attributed 
to the sulphate of potash they contain. Turf ashes are 
also said to contain this salt in variable quantity, and 
to this is ascribed their efficacy when applied to land." 
(Johnston.) 

NITRATE OF SODA, 

N05+NaO=S6, 

Nitrate of soda may be produced by the action of ni- 
tric acid upon carbonate of soda. It is sometimes form- 
ed in the soil in the same manner that the nitrates of 
potash and lime are, in the saltpetre grounds. Exten- 
sive deposites of this salt are found in Chili and Peru 
upon the surface, and from these localities much of the 
nitrate of soda of commerce is obtained. This salt is 
somewhat deliquescent and very soluble in water. Its 
action in promoting vegetation is quite similar to that 
of the nitrate of potash, since the nitric acid contained 
by each is principally concerned in hastening the growth 
of the plant. The soda and potash, however, are by 
no means unimportant. The nitrates of soda and pot- 
ash have been applied in Europe with varied results. 
The following are the effects produced as given by 
Johnston. 

*' The first visible effect ofthe nitrates upon every crop 

What elements does it supply to the plant ? Give the substance of 
the statement of Johnston. How may the nitrate ot soda be formed? 
Whence is much of the nitrate of soda of commerce derived? What is 
said of the nitric acid of the nitrates of potash and soda ? 



76 AGRICULTURAL CHEMISTRY. 

is to impart a dark green color to the leaves and stems. 

2d. They hasten, increase, and not unfrequently 
prolong the growth of the plant. 

3d. They generally cause an increase both in the 
weight of hay or straw, and of corn, though the color 
and growth are occasionally affected without any sen- 
sible increase of the crop. 

4th. The hay or grass produced is always more 
greedily eaten by the cattle than that which has not 
been dressed, even when the quantity is not affected ; 
but the grain is usually of inferior quality, bringing a 
somewhat less price in the market, and yielding a 
smaller produce of flour. 

Its principal action seems to be expended in promo- 
ting the growth— that is, increasing the production of 
woody fibre, either in the stem or the ear, without so 
much affecting, except indirectly, the quantity of seed. 

Mr. Pusey observed, that the increase of his wheat 
crop, on the Oxford clay, where nitrate of soda was 
applied, arose from there being no underling straws 
with short ears as in the undressed, but all were of equal 
length, and consequent fullness and ripeness. The ni- 
trate had merely promoted the growth. 

" It affected the tops of the potatoes, but the produce 
of bulbs was less both by weight and measure." (Mr. 
Grey, of Dilston.) *• On peas, in a thin sandy soil, sub- 
soil gravel, it had much effect on the color and strength 
of the stems, and on the state of forwardness, but when 
ripe, though the straw was stronger, there was no dif- 
ference in the crop of peas." (Col. Campbell, of Ro- 
selle.) " On land in high condition it did harm by for- 
cing the straw at the expense of the ear." (Mr. Bar- 
clay.) " It appeared to act strongly, and there was a 
greater bulk of straw, but the increase of grain was 

State the different effects of the nitrates 1 Do the nitrates seem to in- 
crease the quantity of seed ? 



f 

/ 



4 



NiTJlATE OF SODA. 77 

only 50 lbs. per acre." (Sir Robert Throckmorton.) 
in another experiment of Mr. Barclay's the straw was 
very strong, and much of the wheat laid, but the un- 
dressed sold for 4s. a bushel more, and there was no 
profit. 

In all these cases the nitrate promoted chiefly the 
growth of the stem, or the production of woody fibre. 
The inferior quality of grain, and great yield of straw, 
was owing to this action. The grain was enveloped in a 
thicker covering of the woody matter which forms the 
skin or bran. 

From the above statements we seem to derive an 
explanation why the effects of the nitrate should have 
been so universally observed upon the grasses and clo- 
vers — while in regard to its application to corn crops, 
they indicate this important — 

Practical Rule.— Not to apply the nitrates upon land 
or under circumstances where there is already a suffi- 
cient tendency to produce straw. 

Effect of the nitrates on tJie auALiTY of the crop. 

It so affects the grass and clover as to make it more 
relished by the cattle. This is usually expressed by 
saying that the crop is sweeter, but since cattle are 
known to be fond of saline substances, it may be that 
the grasses are, by these salts, only rendered more sa- 
vory. It generally also gives a grain (of wheat) of an 
inferior quality, which has a thicker skin, and yields 
more bran. This may possibly arise from its having 
been generally allowed to ripen too long. A question 
still undetermined is, whether the flour of nitrated corn 
is more nutritive than that obtained from corn which 
has been undressed." 

What practical rule is deduced from the results of various experiments! 
State the effects of the nitrates upon the quality of the crop 1 What 
question is still undetermined 1 



78 AGRICULTURAL CHEMISTRY. 

CARBONATE OF SODA. 

C02+NaO=54. 

The appearance of carbonate of soda is familiar to 
all in the form of the common soda of commerce. When 
crystalized, it contains ten proportions of water, and its 
symbol would be C Oa+NaO+lO, Aq=144, but the 
crystaline carbonate, when exposed m dry d\v, effloresces, 
or loses its water of crystalization, and becomes a dry 
white powder. This salt is manufactured upon a large 
scale from common salt, (chloride of sodium.) It may 
be obtained also from the ashes of marine plants, as 
carbonate of potash is from those of land plants. The 
action of this salt as a fertilizer has been found favorable, 
especially upon certain plants. It is stated by Johns- 
ton, that the carbonates of potash and soda greatly has- 
ten the growth of the strawberry, and by Sprengel, 
that the carbonate of soda assists in a remarkable man- 
ner the growth of buck-wheat. The presence of soda 
is essential to the perfection of the plant ; the first effect 
of the carbonate therefore will be to supply a necessary 
constituent to the plant, but its action is by no means 
confined to this : it has much to do with preparing oth- 
er substances to become food for the plant. By its ac- 
tion the vegetable matter in the soil become"S soluble, 
and is thus fitted to enter into the circulation of the 
plant. Carbonate of, potash produces the same effect, 
but both of these compounds probably exert a more 
important influence by rendering soluble the silica and 
insoluble silicates of the soil. When speaking of the 
silicate of potash, the manner in which the insoluble 

What is the chemical constitution of carbonate of soda? When crys- 
talized what does it contain ? From what is it usually obtained ? 
What is its effect upon buck- wheat? What effect does it produce upon 
vegetable matter 1 What effect is produced by the carbonates of potash 
and soda upon silica, &.C.] 



J 



SULPHATE OF SODA, OR GLAUBER'a SALT. TO 

compounds are rendered soluble, was pointed out. A 
solution of carbonate of soda in water has the same 
power of uniting with silica, or of decomposing insolu- 
ble silicates, producing the following compound. 

SILICATE OF SODA. 

This compound, in its properties and action upon 
vegetation, is quite similar lo the silicate of potash. It 
has been seen that silica is totally insoluble in water, 
and therefore can not enter into the plant in its uncom- 
bined state. It is probable that nearly all of the silica 
of plants enters in the form of silicates of potash and 
soda, for the solutions of these salts in water slowly 
unite with silica, and form soluble compounds. Al- 
though the silicates have not been applied to any great 
extent as manures, except as they occur in small quan- 
tities in wood ashes ; yet it seems probable that they 
might be manufactured so as to be economically used 
as fertilizers. The silica plants especially, would be 
greatly aided by such manures. 

SULPHATE OF SODA, OR GLAUBER'S SALT. 

S03+NaO=72. 

Glauber's salt in its common form, like carbonate of 
soda, contains ten proportions of water, but loses it by 
effloresence, and becomes a white powder. In the pro- 
cess given for obtaining muriatic acid from common 
salt, (page 51) the sulphate of soda is formed in the 
flask. This salt is always obtained in large quantities 
in the manufacture of muriatic acid. 

What does soda form by combination with silica? Why are the sili- 
cates important? Where do they occur? What is the chemical con- 
stitution of Glauber's salt ? What is said of the manufacture of muriatic 
acid ? 



80 AGRICULTURAL CHEMISTRY. 

In the manufacture of carbonate of soda from com- 
mon salt, (see page 78) the sulphate is first formed, and 
after being mixed with pulverized chalk and charcoal, 
exposed to a red heat ; the carbonate thus produced is 
dissolved out, and the solution crystalized. 

The action of the sulphate of soda upon vegetation 
is like that of the sulphate of potash. But the soda salt 
can be applied much more economically than that of 
potash, as it is aflbrded at a much lower price. Both 
salts are found in the ashes of plants. These compounds 
have the most favorable effect upon those plants that 
contain most sulphuric acid. Instances are given by 
Johnston, in which their application as manures result- 
ed in a marked increase of the crop, 

NITRATE OF LIME. 

N03+CaO=82. 

Nitrate of lime is a very deliquescent salt, and may 
be formed by the action of dilute nitric acid upon chalk ; 
the solution after being evaporated to a syrup crystal- 
izes. All the nitrates are formed in considerable quan- 
tity in nature, and the manner in which they are pro- 
duced has been pointed out ; but it may not be impro- 
per to introduce in this connection, a more full explana- 
tion of the changes connected with their formation. It 
is made evident by experiment, that nitric acid can be 
formed by the chemical combination of the gases oxy- 
gen and nitrogen as they exist in the atmosphere. In 
confirmation of this, we find a portion of nitric acid, 
combined with ammonia, in the water that falls during 
thunder showers. The combination of elements is pro- 
duced in these instances by atmospheric electricity, but 

Upon what plants do the sulphates act most favorably ? How may 
nitrate of lime be formed] How is nitric acid sometimes formed 1 



f 



f 



NITRATE OF LIMB. 81 

it would appear that nitric acid is often produced in 
ordinary weather, and when there is no exhibition of 
electrical phenomena. This result seems to be produ- 
ced whenever those substances that contain nitrogen 
are undergoing decomposition. All animal, and most 
vegetable substances give off ammonia in process of 
decomposition: the nitrogen of the ammonia seems to 
unite with the oxygen of the air, forming nitric acid, 
and, this, combining with the various bases contained in 
the soil, forms the nitrate of lime, potash, soda, &c. 
This is the process continually going on in those places 
where the nitrates accumulate so extensively, and the 
reason why they occur so abundantly is, that in these 
localities there is a greater abundance of animal and 
vegetable matter in the soil, that is slowly suffering de- 
composition. Any accumulation of decaying organic 
matter, accompanied by a sufficient quantity of earth, 
to supply the necessary bases, is to a certain extent a 
nitre bed. Compost heaps are of this nature. 

Nitrate of lime is most generally formed in those lo- 
calities where nitric acid is produced, because lime is 
almost always present in the soil. This nitrate occurs 
also in the limestone caverns of the west and south west, 
and from it large quantities of nitre are formed. Ni- 
trate of lime is converted into saltpetre by the mixture 
of wood ashes with the earth containing the former salt: 
the nitric acid combining with potash leaves the lime. 

The process for forming nitric acid was omitted in 
treating of the primary compounds, because the sub- 
stances from which it is derived had not been examined. 
The acid may be formed from either of the nitrates, 
but of late ha^s been obtained mostly from the nitrate of 
soda. 

How is it formed in ordinary weather? With what does it combine ? 
Why do the nitrates occur so abundantly in certain localities ? What 
nitrate is most generally formed 7 How is nitrate of lime converted into 
saltpetre 1 From what is nitric acid usually obtained ] 



82 AGRICULTURAL CHEMISTRY, 

To prepare the acid, one part of strong sulphuric 
acid is poured upon two of nitrate of soda contained in 
a glass retort, and the mixture is subjected to heat; the 
acid, distilling over, condenses in a receiver cooled by 
the external application of cold water. Nitric acid has 
never been obtained free from water, and the commer- 
cial acid contains it in considerable quantity. 

The action of nitrate of soda as a fertilizer, is similar 
to that of the other nitrates, but it can not be economi- 
cally obtained for agricultural purposes, except in lo- 
calities where it is rapidly formed by natural causes. 
Compost heaps, however, may be formed in which the 
different nitrates will accumulate to some extent. The 
agriculturist should recollect that the action of the ni- 
trates is not favorable upon all crops and under all cir- 
cumstances : since they sometimes increase the straw, 
at the expense of the seed, (see page 76.) Johnston sug- 
gests that the presence of lime in the soil, tends to in- 
sure the success of the nitrate ; if so, it is probable that 
the nitrate of lime is a more valuable fertilizer than that 
ot soda or potash. 

CARBONATE OF LIME. 

CO2-fCaO=-50. 

Chalk, limestone, and marble, different forms of the 
carbonate of lime, occur in immense quantities in the 
mineral crust of the earth, and are familiar to all. Car- 
bonate of lime is insoluble in pure water, but water, 
saturated with carbonic acid dissolves about tjV o^ ^^ i^s 
weight of this substance. The water of springs, wells, 
&c., generally contains this acid, and hence we find a 

Give the process. What is said of the action of nitrate of soda as a 
fertilizer? What is said of compost heaps ] What effect is sometimes 
produced by the nitrates 1 Mention the different forms of carbonate of 
lime. Is the carbonate soluble in pure water ? In what is it soluble ? 



/ 



/ 



CARBONATE OF LIME. 83 

portion of lime dissolved in such water, but when ex- 
posed for a length of time to the air, the carbonic acid 
passes off and the carbonate of lime is deposited. In 
petrifying springs, as they are called, this process is 
continually going on. The water, as it percolates through 
the limestone strata, dissolves a portion of the carbonate, 
but when it 'gushes from the hill side, or trickles from 
the rock, its carbonic acid is dissipated, and the carbon- 
ate of lime is deposited in exceedingly minute particles. 
When these particles come in contact with decaying 
vegetable matter, they gradually take the place of the 
disappearing atoms, and eventually produce in lime- 
stone an exact copy of the plant ; in like manner animal 
forms are petrified. 

Lime is an essential constituent of vegetable forms, 
and constitutes a large percentage of the ashes of cer- 
tain plants ; these are called lime plants. It is from the 
carbonate, without doubt, that lime is principally sup- 
plied to the plant, for, notwithstanding lime is often 
applied to soils in its caustic state, — -having been freed 
from its carbonic acid by heat — yet it is very soon 
changed to a carbonate again by combination with 
the carbonic acid of the atmosphere. It would seem, 
then, entirely unnecessary to expel the carbonic acid, 
as is done in the lime kiln, if the lime is to be applied 
merely as food for the plant. Indeed it is certain that, 
in most cases, the only benefit arising from burning 
lime that is to be used for agricultural purposes, is this : 
the rock is thus rendered easily reducible to a fine pow- 
der, but in this point of view it is not necessary to have 
recourse to burned lime, since the various marls that 
occur in such vast quantities, are in a sufficiently finely 
divided state, and can be applied with little trouble. 

When spring water is exposed to the air what follows? Describe the 
process continually going on in petrifying springs. What are lime plants? 
What change takes place in caustic lime applied to the soil ? What 
benefit arising from burning lime ? What may be substituted for it ? 



\ 



84 AGRICULTURAL CHEMISTRY. 

The carbonate in this form may be in ordinary cases, 
as profitably used as the more expensive burned lime. 
Caustic lime, as is stated elsewhere, is required when- 
ever animal or vegetable substances are to be decom- 
posed rapidly, and slacked lime may be applied when 
the same decomposition is to be gradually eflfected, but 
when lime is to be supplied merely as food for the plant, 
there is no advantage in applying it in the form of quick- 
lime. Marl may be obtained by most farmers with 
little difficulty, and is the cheapest form in which the 
carbonate can be applied. But the action of the car- 
bonate is not confined to supplying lime directly to the 
plant ; it possesses the same power of decomposing 
vegetable matter that is possessed by caustic lime, 
though not to that degree. Certain acids are produced 
during the decomposition of vegetable matter that have 
the effect of arresting the further decay of those sub- 
stances, and in addition to this, are prejudicial to the 
growing plant. These acids decompose the carbonate, 
uniting with its lime, and gradually releasing the car- 
bonic acid. Thus the unfavorable action of the vege- 
table acids is prevented, and carbonic acid is supplied 
to the plant. 

The various modes in which the carbonate acts, will 
be more fully treated of hereafter, 

SILICATE OF LIME. 

The silicate of lime occurs as a constituent of certain 
minerals, and since soils arise from the disintegration 
of the various mineral masses, it follows that this sili- 
cate is, to some extent at least, a constituent of the soils. 
It occurs in the ashes of plants. 

When is caustic lime required 7 What is said of the action of a car- 
bonate 1 What effect does it have upon certain acids ? Is silicate of 
lime a constituent of soils ? 



SILICATE OF LIME. 85 

On account of the insolubility of this silicate, it does 
not directly supply nourishment to the plant, but like 
the other silicates, is slowly decomposed by the carbonic 
acid of the atmosphere, thus, eventually supplying both 
carbonate of lime and silica to the plant. It will be 
recollected that when silica is first released from its 
combination with the various bases, it is to some ex- 
tent soluble in pure water, and the solutions of potash, 
soda, (fee, readily combine with it in this state, forming 
soluble silicates in the soil. The action of silicate of 
Jime upon vegetation, depends upon this process of de- 
composition, but it is not decomposed by carbonic acid 
only ; the acids which are formed during the decay of 
vegetable substances, by combination with the lime of 
this silicate, release the silica ; by this union the acids, 
before hostile to. vegetable life, are rendered harmless. 

Lime and sand mixed as in the preparation of mor- 
tar unite chemically, producing the silicate of lime, 
and the same effect is produced to a certain extent, 
when lime is applied to siliceous soils. This compound 
is not only useless as long as it remains undecomposed, 
but is really injurious w^hen remaining unchanged in 
considerable quantity in the soil. If then lime be ap- 
plied to sandy land those substances should accompany 
it which will ensure its decomposition, for the carbonic 
acid of the air alone will not produce the requisite 
change. Vegetable matter supplies carbonic acid and 
other decomposing substances to the insoluble silicates, 
and thus provides ample means for accomplishing the 
required decomposition. Lime, then, should always be 

Is it a soluble salt ? By what is it slowly decomposed ? With what 
does the carbonic acid unite ? What compound is formed ? What is 
said of silica when first released from its combinations? What is said 
of other decomposing agents besides carbonic acid ? What compound is 
formed in the preparation of mortar 1 When is the same compound 
formed in the soil 1 What direction are given with reference to the ap- 
plication of lime to siliceous soils 1 



86 AGRICULTURAL CHEMISTEYi 

accompanied by vegetable matter in some form when 
applied to light soils, unless there is already an accu- 
mulation of such matter in the soil. 

It has been observed that the soils formed by the dis- 
integration of those rocks which contain the silicate of 
lime, are exceedingly fertile, but most soils are derived 
from rocks that contain very little of this compound. 
Those varieties of lime stone which contain a portion 
of sand, would probablv prove most valuable as a fer- 
tilizer ; in such the silex and lime sometimes combine 
during the process of burning, and the silicate of lime 
is formed. 

SULPHATE OF LIME, GYPSUM, OR PLASTER, 

S03+CaO=68. 

By the action of sulphuric acid upon lime or any solu- 
ble salt of lime, the sulphate of this base is produced. 
It is not necessary, however, to prepare it artificially, 
as it occurs in various forms and in immense quantities. 
The common plaster is an impure form, containing an 
admixture of earthy matter; it occurs as the part of the 
rock formations of the New York system, not in beds 
or layers, but in detached and irregular masses. There 
is a purer, crystalized variety of this salt called gypsum, 
which, exposed to heat, loses the two proportions of 
water usually contained by it, and is changed to a dry 
white powder called pZ«5ier of Paris, In this state, it 
is fitted for giving a hard finish to walls or for produ- 
cing plaster casts, &c. In these operations the plaster 
sets, as it is termed, by virtue of its avidity for moisture ; 
the water which has been driven off by heat is rapidly 

What is the nature of soils containing the silicate of lime 1 Give the 
chemical constitution of the sulphate of lime. Mention the different va- 
rieties found in nature . What effect is produced upon gypsum by expo- 
sure to heat ? What causes plaster of Paris to set 7 



SULPHATE OF LIME, GYPSUM, OR PLASTER. 87 

taken up when mixed with the plaster, and the expan- 
sion of the mixture produces an exact copy of the 
mould. Alabaster is another form of the sulphate quite 
pure and translucent. 

This salt of lime is slightly soluble in water ; a gallon 
of this fluid dissolving about one quarter of an ounce of 
the sulphate. 

Sulphate of lime is one of the most valuable fertilizers, 
and can generally be obtained at a price that will ad- 
mit of its being economically applied to the soil. It is 
found in the ashes of plants, and is a constituent of most 
soils, although generally occurring in minute quantities. 
Its presence is absolutely requisite to the perfection of 
the plant, and since it is sparingly disseminated in the 
soil it is not strange that the application of it to the 
growing crop has produced favorable results. Those 
crops are most benefited which contain most of the sul- 
phate in their ashes. Yet it must not be inferred that 
the only office of this compound is, to supply food to 
the plant from its own substance. Its action in decom- 
posing the carbonate of ammonia and giving to the 
volatile gas ^ fixed form, is probably more important 
than the mere act of supplying sulphate of lime to the 
plant. The following experiment given by Petzholdt 
illustrates the changes produced by gypsum upon car- 
bonate of ammonia. 

" A small plot of garden ground was manured with 
fresh horse-dung, and then sowed with peas and beans 
— the surface was then covered with a thin layer of 
uncalcined gypsum. The ground was protected from 
rain, and watered in dry weather. All the beans and 
peas grew up with extraordinary rapidity and luxuri- 
ance. Before commencing the experiment, the soil, as 

What is said of the solubility of this sulphate ? Of its importance as 
a fertilizer? What crops are most benefited? Give the effect of this 
sulphate upon carbonate of ammonia ? 



m: 



88 AGRICULTURAL CHEMISTRY. 

well as the gypsum, was accurately tested, and ex- 
hibited not the slightest trace of a carbonate. But when 
after the lapse of three weeks, the gypsum was remov- 
ed from the surface and tested, the greater part of it 
was found to have become transformed into carbonate 
of lime ; the whole soil to the depth of six inches effer- 
vesced strongly with acids. The soil was lixivated 
with cold water, the fluid filtered, and after evaporation 
a considerable amount of sulphate of ammonia remain- 
ed. The very slight solubility of gypsum in water, and 
the slowness of its decomposition by carbonate of am- 
monia, explain the favorable action of gypsum as a 
manure, and the reason why its effects are not transi- 
tory but remain for years." 

It seems then, that when sulphate of lime and car- 
bonate of ammonia are in contact, double decomposition 
ensues ; the sulphuric acid of the former uniting with 
the ammonia of the latter, forms sulphate of ammonia; 
the carbonic acid and remaining base, form carbonate 
of lime. In this process, ammonia is changed from a 
volatile to a fixed form, and is thus retained for the 
nourishment of the plant. 

Since this sulphate requires a considerable portion of 
water to dissolve it, its action upon dry soils will not 
be as apparent as upon those supplied with the requisite 
degree of moisture. The sulphates of potash and soda 
produce the same effect upon vegetation as that of lime, 
as far as a supply of sulphuric acid is concerned, and 
it is probable that they even form the sulphate of lime 
in the soil, whenever lime is present to decompose these 
salts, but gypsum can be obtained at much less expense 

To what was the sulphate of lime changed in the experiment given ? 
What was obtained from the soil 1 What decomposition is produced 
when carbonate of ammonia and sulphate of lime are in contact ? How 
is ammonia effected in this change ? What is said of the action of sul- 
phate of lime upon dry soil ? What is said of the sulphate of potash and 
•soda ? 



fHOSFHATE OF LIME- 89 

than the other sulphates, and hence, is preferable as a 
fertilizer ; there may be cases, however, in which the 
application of the more soluble sulphates will be advi- 
sable, as upon very dry soils where there is not suffi- 
cient moisture to dissolve the sulphate of lime« 

If the action of plaster is such as is indicated by ihe 
experiment ^iven, the importance of its application to 
all places where ammonia is produced, is evident. If 
it be strewed upon the floors of stables, mixed with 
manures, or spread over the surface of compost heaps, 
it will effectually secure that element which otherwise 
will pass quickly away, and be disseminated in the at- 
mosphere. 

PHOSPHATE OF LIME. 

This compound of phosphoric acid and iime occurs 
in bones, constituting about 50 per cent, of their weight. 
The mineral called apatite is nearly pure phosphate of 
lime. 

Phosphorus is an element of plants, and the only 
source from which it can be obtained is phosphoric 
acid, in its combinations with ammonia, lime, &c. It 
has been stated before, that the ferlilizing power of 
guano, urine, &c., depends upon the presence of the 
phosphates. Bone dust probably owes its value as a 
fertilizer in most instances, to the presence of the phos- 
phate of lime ; upon this point, however, there seems to 
be something of a difference of opinion, as the following 
remarks of Johnston will indicate. 

*' When bones are buried in a more or less entire 
state, as they occasionally are about the roots of vines 
and fruit trees, they gradually decay, and sensibly pro- 
mote the growth of the trees to which they are applied. 

In what cases will they act more favorably than sulphate of lime ? 
Where should plaster be applied 1 Where does the phosphate of lime 
occur] To what is the fertilizing power of guano, &-c. owing ? 

*2 



90 AGRICULTURAL CHEMISTRY. 

Yet after the lapse of years these same bones may be 
dug up nearly unaltered either in form or in size. The 
bones of a bear, after being long buried, were found by 
Marchand to consist of 



BONES OF THE 


BEAR 


BURIED, 








Deep. 


Shallow. 


Animal matter, 




162 


4-2 


Phosphate of lime, 




56-0 


62-1 


Carbonate of lime. 




13-1 


13-3 


Sulphate of lime, 




7-1 


12-3 


Phosphate of magnesia, 




0-3 


0-5 


Fluoride of calcium. 




20 


21 


Oxide of iron and mang 


anese. 


, 2-0 


2-1 


Soda, 




1-1 


1-3 


Silica, 




2-2 


21 



100 100 

The most striking change undergone by these bones 
was the large loss of organic or animal matter they had 
suffered. The relative proportions of the phosphate 
and carbonate of lime had been comparatively little 
altered. The ??2«m effect, therefore, produced by bones 
when buried at the roots of trees, and their^rs^ effect 
in all cases, must be owing to the animal matter they 
contain — the elements of this animal matter, as it de- 
composes, being absorbed by the roots with which the 
bones are in contact. 

Such facts as this prove, I think, the incorrectness of 
the one-sided opinion too hastily advanced by Sprengel, 
and after him reiterated by Liebig and his followers — 
that the principal efficacy of bones is, in all cases, to be 
ascribed to their earthy ingredients, and especially to 
the phosphate of lime." 

What difference of opinion has arisen with regard to bone dust ? In 
the experiment given what loss did the bones suffer? 



PHOSPHATE OF LIME. 91 

Probably this difference of opinion arises from con- 
sidering the bones in different states ; they contain be- 
sides phosphate of hme, nearly 50 per cent, of animal 
matter, rich in nitrogen. If the bones be crushed while 
they yet retain this matter, their influence upon vegeta- 
tion will be favorable, on account of the supply of am- 
monia yielded by the decomposition of the more de- 
structible part of the bone, and the effect produced will 
be more immediately perceived than if the pure phos- 
phate is applied. By boiling, a portion of animal mat- 
ter is separated from the bones, and they are rendered 
less valuable: yet this process seems to fit them for 
more rapid decomposition, and therefore their effect 
when applied to the soil is often quite as marked as that 
of the unboiled. 

When bones are burned that they may be the more 
easily pulverized, all the gelatinous matter is driven off 
and the remaining mineral mass is mostly phosphate of 
lime. The bone dust thus obtained, when applied to 
soil destitute of the phosphates, produces exceedingly 
favorable results. Jf there is already a supply of phos- 
phate of lime in the soil, this form of bone earth will 
produce no effect, but those forms which contain a por- 
tion of animal matter, will promote vegetation even 
when no phosphate is required, and in such cases the 
result will be seen to indicate that the phosphate of the 
bones is of comparatively little importance. 

Whenever the compounds of phosphoric acid are 
wanting in the soil, the application of bone dust, in any 
state, will greatly promote the growth of the plant by 
supplying phosphoric acid. 

The difference of opinion which we have noticed, has 
arisen from the difference of circumstances under which 

What inference is drawn from this experiment ? State the different 
modes of preparing bones? What is said of bone dust that contains no 
animal matter 1 



92 AGRICULTURAL CHEMISTRY. 

experiments have been conducted ; Liebig, however, 
does not' suppose the gelatine of bones of no effect upon 
vegetation, as is evident from the following remarks. 

" One hundred parts of dry bones contain from 32 to 
33 per cent, ot dry gelatine ; now, supposing this to con- 
tain the same quantity of nitrogen as animal glue, viz. 
5*28 per cent., then one hundred parts of bones must 
be considered as equivalent to two hundred and fifty 
parts of human urine. 

Bones may be preserved unchanged for thousands of 
years, in dry or even in moist soils, provided the ac- 
cess of rain is prevented, as is exemplified by the bones 
of antedeluvian animals found in loam or gypsum, the 
interior parts being protected by the exterior from the 
action of water. But they become warm when reduced 
to a fine powder, and moistened bones generate heat 
and enter into putrefaction ; the gelatine which they 
contain is decomposed, and its nitrogen converted into 
carbonate of ammonia and other ammoniacal salts, 
which are retained in a great measure by the powder 
itself. (Bones burnt till quite white, and recently heat- 
ed to redness, absorb 7*5 times their volume of pure 
ammoniacal gas." 

Both authors from whom we have quoted upon this 
point, are convinced of the two-fold action of crushed 
bones, but one considers the organic part of them more 
efficacious, the other thinks the mineral portion more 
beneficial to vegetation. It seems probable, that when- 
ever a supply of the phosphate is demanded, the soii 
being destitute of it, bone dust is principally useful on 
account of its mineral constituents. 

Some marls contain a portion of the phosphate of 
lime, and to the presence of this their favorable influ- 
ence upon vegetation may, in part, be attributed. 

What is Liebig's view with respect to the effect of the gelatine of 
bones 1 Burnt bones absorb what ] What is said of some marls 1 



CAKBONATE OF MAGNESIA. 93 

NITRATE OF MAGNESIA. 

N05+MgO=74. 

This salt may be prepared by dissolving carbonate 
of magnesia in nitric acid, and evaporating the solution. 
It is formed in nature in the same way that the other 
nitrates are produced. Its action upon vegetation is 
like that of the nitrates of lime *as far as a supply of 
nitrogen to the plant is concerned ; certain of the more 
soluble salts of magnesia, however, have been supposed 
to act unfavorably, when occurring in the soil in too 
great quantities. 

The nitrates of magnesia can be easily decomposed 
by potash, as is the nitrate of lime in the manufacture 
of nitre. 

A supply of magnesia is requisite to the perfect de- 
velopment of the plant. Yet care must be taken that a 
limited quantity be applied ; it is not generally applied 
in the form of the nitrate, except as this salt may occur 
in the compost heap. The following is the most com- 
mon salt of magnesia. 

CARBONATE OF MAGNESIA. 

C02 4-MgO=42. 

It has been before stated that magnesia occurs in cer- 
tain mineral masses called magnesian limestones ; in 
these it is found in the form of a carbonate. When 
those varieties of limestone which contain magnesia 
are applied to the soil, the result is sometimes unfavor- 
able on account of the union of certain acids, with the 

How is nitrate of magnesia formed in natural What is said of its ac- 
tion upon vegetation ? How may the nitrate of magnesia be decom- 
posed ] 



i»\ 



94 AGRICULTURAL CHEMISTRY. 

base formin;^ soluble compounds unfavorable to vege- 
tation. 

When magnesian limestone is burned, the magnesia 
is rendered caustic, as well as the lime, and by its mix- 
ture v^ith the silica of the soil, has a tendency to form 
a hard mortar, thus rendering the soil stiff and in a 
measure impenetrable, preventing the extension of the 
roots of the plant. Carbonic acid does not unite as 
readily with magnesia as it does with lime, and there- 
fore the former substance remains in a caustic state 
longer than the latter ; the unflivorable action of mag- 
nesia in large quantities may be, in part, owing to this. 
The magnesia of commerce is generally in the caustic 
form, but if exposed to the air will be changed gradually 
to the carbonate. 

SILICATE OF MAGNESIA. 

The silicate of magnesia occurs in certain mineral 
forms, of which the most common are soapstone and 
serpentine; soils therefore contain this compound, at 
least in some localities. On account of the insolubility 
of this silicate, it can not under ordinary circumstances 
prove hurtful to vegetation, but on the contrary, as it is 
slowly decomposed by carbonic acid, will provide both 
silica and magnesia to the growing plant. 

SULPHATE OF MAGNESIA, OR EPSOM SALTS. 

SO3-MV[gO=60. 

This salt is manufactured in large quantities from 
sea water, in connection with the manufacture of com- 
mon salt ; the latter substance is first separated by 

What is the effect of burning magnesian limestone 1 When this mix- 
ture is applied to the soil what is the result 1 Why does magnesia act 
unfavorably on vegetation? In what mineral does the silicate of mag- 
nesia occur? What will this compound supply to the plant ] 



SULPHATE OF MAGNESIA, OR EPSOM SALTS. 95 

evaporating the water until only a small portion re- 
mains and removing the crystalized salt; the remaining 
fluid is called mother liquor, or bittern, and contains 
sulphate and carbonate of magnesia ; by supplying sul- 
phuric acid, ihe latter is decomposed and the sulphate 
formed ; from this solution the salt is obtained by evap- 
oration. 

Sulphate of magnesia is also obtained by dissolving 
magnesian limestone in dilute sulphuric acid ; the inso- 
luble sulphate of lime formed at the same time, is easily 
removed and from the remaining liquid the salt is ob- 
tained by evaporation. The common ijame Epsom 
salts is derived from the place Epsom, vv^here the min- 
eral waters contain this salt. 

The application of this substance as a fertilizer, in the 
few cases of which we have any knowledge, has re- 
sulted favorably ; its action being similar to that of the 
other sulphates, but it can not be economically applied 
at present. 

Phosphate of magnesia. — This compound of phos- 
phoric acid and magnesia, although not of common 
occurrence, is obtained in the analysis of plants, being 
contained especially in the grains of wheat, rye, &c., and 
is an important constituent. Bone earth contains a por- 
tion of this phosphate, and it also occurs in minute 
quantity in certain manures. It is supposed, however, 
that the phosphoric acid and magnesia are generally 
obtained by the plant from different sources, and are 
combined within the plant, forming this compound. 

What is the chemical constitution of Epsom salts ? By what process 
is it obtained from sea-water ? From what other source is it obtained 1 
Has it produced favorable results when applied to the soil ? Where does 
phosphate of magnesia occur 1. 



96 AGRICULTURAL CHEMISTRt: 

SULPHATE OF IROX, OR COPPERAS. 

S03+FeO=76. 

This well known salt may be formed by dissolving 
iron in dilute sulphuric acid, and evaporating the solu- 
tion. In its ordinary crystaline state it contains seven 
atoms of water which it yields up when exposed to heat. 
Copperas is frequently formed in soils that contain a 
certain compound of sulphur and iron, called bisulphu- 
ret of Iron ; by the presence of air and moisture the 
sulphur of this' compound is converted into sulphuric 
acid which, uniting with the iron, forms the sulphate of 
that metal. The presence of this salt in considerable 
quantity, is unfavorable to vegetation, but it may be 
easily decomposed by quicklime. 

CARBONATE OF IRON. 

C02+FeO=58. 

The sulphate of iron just described, may be decom- 
posed by carbonate of soda; the carbonic acid of the 
latter compound uniting with the iron, forms carbonate 
of iron. Whenever the sulphate occurs in the soil, it 
is slowly decomposed by the carbonates. Carbonate 
of iron is slightly soluble in water containing carbonic 
acid, and when dissolved by it, enters into the plant; 
probably most of the iron essential to the plant, is ob- 
tained in this way. 

What is the chemical name of copperas ? How may it be obtained ? 
How is it formed in soils ? What is its effect when occurring in excess ? 
How may this salt be decomposed ? When decomposed by carbonate of 
soda what is formed ? In what form does iron enter the plant ? 



SILICATE OF ALUMINA. 97 



SALTS OF MANGANESE. 

Manganese is an essential constituent of plants, al- 
though it is found in very minute quantities in their 
ashes, and since the oxides of this metal are insoluble 
in water, a supply must be obtained from some other 
compounds. 

The sulphate of manganese is sometimes formed in the 
soil ; and its presence in limited quantity, is without 
doubt favorable to vegetation. 

The caiiionate of manganese, is formed from the sul- 
phate, and is soluble in certain acids usually existing in 
the soil; these soluble compounds supply manganese to 
the plant. 

SILICATE OF ALUMINA. 

Alumina as it exists in the soil generally has a portion 
of silica combined with it, forming the silicate of alum- 
ina, this is the composition of the various clays, and the 
majority of all minerals contain this silicate. The dif- 
ferent varieties of porcelain, china,, and earthen ware 
are silicates of alumina, more or less pure. 

The presence of this compound in the soil is neces- 
sary, to render it sufficiently retentive of moisture ; but 
from its insolubility probably does not directly supply 
food to the plant. ^Allusion has been made to the fact, 
that alumina possesses the property of absorbing am- 
monia, and doubtless it is an important office of clay, to 
supply ammonia to the plant. If, however, the clay is 
too compact, it seems to retain the ammonia with too 
much force. The application of lime, will to a certain 
extent, remedy this. 

Are the oxides of manganese soluble ? Does sulphate of manganese 
occur m soils ? What is said of carbonate of manganese ? In what 
form does silica exist in the soil 1 What is said of porcelain ware, &c. t 
What important office does clay perform ? What must be applied when 
clay is too compact ? 
J 



98 AGRICULTURAL CHEMISTRY. 

General action of the silicates. —The great import- 
ance of silica in the production of vegetable formsy 
renders a few general explanations necessary with re- 
spect to the manner in which the silicates promote veg- 
etation. It has been stated that pure silica, in its ordi- 
nary state, is insoluble in water, yet it is a peculiarity 
of this substance, to which allusion has been made, 
that it is under certain circumstances, slightly soluble. 
If the soluble glass described on page 73 be decom- 
posed by applying an acid, the silica will be deposited 
in a soft gelatinous state ; this form of silica, before it 
it is dried, is soluble in water, or in solutions of the al- 
kalies, potash, soda, &c., but after it has been thorough- 
ly dried it becomes insoluble again. The insoluble 
silicates of lime, magnesia, potash, soda, &c., are slow- 
ly decomposed by carbonic acid and other agencies, 
and the silica is separated in this gelatinous, soluble 
state; in this form it can be taken up by the plant dis- 
solved in water, or. if the alkalies, potash, soda, &C.,. 
exist in a free state in the soil, they combine with the 
silica, forming soluble compounds tliat are absorbed by 
vegetable forms. 

RECAPITULATION. 

For the purpose of fixing in the mind of the learner^ 
the connection and general bearing of the preceding 
pages, a brief recapitulation is here given, of the nature 
of those substances that make up the plant, and the 
sources from which they are derived. 

Elementary substances contained by plants. 

Oxygen, hydrogen, nitrogen, carbon, silicon, sulphur, 
phosphorus, chlorine, iodine, bromine, fluorine, potassi- 

What is said of silica in its ordinary state ? When soluble glass is- 
decomposed in what form is silica deposited ? What peculiar property 
of silica when in this state ? 



RECAPITULATION. 99 

um, sodium, calcium, magnesium, iron, manganese and 
aluminum. 

These elements are sometimes divided into two 
classes, orgardc and inorganic ; those which disappear 
when the plant is burnt in the open air, viz., oxygen, hy- 
drogen, nitrogen, and carbon, are called organic ele- 
ments-, those which remain in the ashes are called inor- 
ganic. 

The organic elements constitute from 88 to 99 per 
-cent, of the plant. 

Properties of the different elements and sources from 
which they are derived. 

Oxygen. — This element is a transparent, tasteless, 
and inodorous gas, a little heavier than atmospheric 
air. It is the great supporter of combustion and res- 
piration, and is essential to both animal and vegetable 
life. 

This gas constitutes from 35 to 45 per cent, of the 
various vegetable substances cultivated for food. 

The source from which oxygen is principally obtained 
is water, which, it will be recollected is a compound of 
oxygen and hydrogen. It may not however be whol- 
ly derived from the constituents of water, for this liquid 
generally contains a small quantity of the oxygen of the 
air dissolved in it, which is conveyed with it into the 
plant, and it is quite possible that a portion of the oxy- 
gen of vegetable substances is thus derived from the 
atmosphere. 

Hydrogen. — This element also is colorless, tasteless, 
and inodorous when pure, and 14 times lighter than air. 

It will support neither combustion nor respiration^ 
but is itself inflammable. 

Hydrogen constitutes from 5 to 7 per cent, of the 
elements of vegetable forms. It will be noticed that ox- 
ygen and hydrogen exist in the plant in nearly the pro- 



AGRICULTURAL CHEMISTRY. 

portions to form water, but that hydrogen is somewhat 
in excess. 

Water is doubtless the principal source from whicii 
this element also is obtained, but it is quite probable that 
it is also supplied by the decomposiition of ammonia, the 
constitution of which isN Hs. 

Nitrogen. — This gas is similar to oxygen and hydro- 
gen in its appearance, and is a little lighter than com- 
mon air. It will not support combustion, and although 
not poisonous in its nature, is not a supporter of animal 
life; we cannot live in an atmosphere of pure nitrogen 
for the same reason that we can not exist for any length 
of time beneath the surface of water- — because there is 
not a supply of oxygen. 

The amount of nitrogen in different plants cultivated 
for food varies from 1 to 7 per cent., and sometimes oc- 
curs in the plant as a constituent of saltpetre which is 
sometimes found in the stem. 

This element is principally obtained from ammonia, 
but may be in part obtained from the air, since all of 
the constituents of the atmosphere are dissolved in the 
water taken into the circulation of the plant. 

Nitrogen is sometimes obtained from the different 
nitrates occurring in the soil, the most common of which 
is saltpetre. In some localities nitrates accumulate in 
immense quantities : and in such places these salts have 
proved hostile to vegetable life ; but in most situations 
a very limited quantity is formed, and in many soils not 
a trace of any of the nitrates can be found. We must 
depend then upon ammonia as the principal source from 
which nitrogen is to be supplied to vegetation. 

In the decay of animal and vegetable forms this gas 
is evolved ; such substances, therefore, should be sup- 
plied to the soil, at the same time Xho^e fixers of ammt- 
nia of which we have before spoken should be applied 
for the purpose of retaining this important elemcut. 



RECAPITULATION. 101 

Carbon — The diamond, charcoal, and black lead, are 
different forms of carbon ; the first pure, the others 
nearly so. 

Carbon constitutes from 40 to 50 per cent, of vege- 
table forms. 

Most soils contain a portion of vegetable matter, 
which consists principally of carbon ; this is gradually 
changed to carbonic acid which is dissolved in water, 
and thus easily conveyed into the vegetable structure ; 
but it is from the atmosphere and not from decaying 
vegetable matter, that plants obtain most of their car- 
bon. During the day the leaves absorb carbonic acid 
from the air, retaining the carbon and returning the 
oxygen. 

Silicon.— T\\\s element is found in plants in combina- 
tion with oxygen, forming silica. It is this that gives 
strength to the slender stalk, and enables it to bear up 
the heavy grain. 

The sources from which silica is derived have been 
pointed out at length ; it is ever derived from the sili- 
cates of lime, potash, soda, &c. 

Sulphur. — This familiar substance is not obtained 
from the plant in its simple form, but is found combined 
with oxygen, forming sulphuric acid, and this acid is 
generally found combined with lime. Sulphate of lime 
is the principal source from which the plant obtains 
this constituent, though other sulphates sometimes occur 
in the soil. 

Phosphorus. — The element phosphorus can not be 
assimilated in its elementary form, and does not occur 
in this form in the ashes of plants : phosphoric acid 
combined with Ume and magnesia are obtained in the 
analysis of plants, and without doubt it is taken up by 
the plant, to some extent, in the form of the different 
phosphates. 



102 AGRICULTURAL CHEMISTRY. 

Chlorine. — The element chlorine is a greenish yel- 
low gas, and in its pure state, destructive of animal and 
vegetable life. It is not assimilated by the plant in its 
elementary state. Combined with the metal sodium, 
forming common salt, (chloride of sodium,) it is detect- 
ed in soils, and from this compound most of the chlorine 
of the plant is derived. Other compounds, such as the 
chloride of calcium, sometimes occur in the soil, from 
which chlorine may be derived. 

Potassium. — It will be remembered that potassium is 
a soft metal that takes fire when thrown upon water, 
absorbing the oxygen of that liquid and being converted 
into potash. This eleaient does not occur in its metallic 
form, and is not obtained from plants in this state, but 
is found in their ashes in the form of potash or salts of 
potash. The vegetable matter of the soil yields a por- 
tion of potash to the plant, in the process of decompo- 
sition, and most soils contain more or less of the salts 
of this base. Whenever soils are deficient in this com- 
pound it may be economically supplied in the form of 
wood ashes. 

Sodium. — This element is a metal, white like silver, 
and in most of its properties similar to potassium. It 
does not occur in its metallic state, either in soils or in 
the ashes of plants. 

Sodium occurs very extensively in nature combined 
with chlorine, forming common salt, and from this com- 
pound, vegetable forms, in part, obtain the element under 
consideration. Soda, a compound formed by the union 
of oxygen with the metal, is also contained in soils, and 
from it this element is readily obtained. 

Calcium. — A white metal derived from lime is called 
calcium. The ashes of plants never contain this ele- 
ment uncombined with others, and it does not occur in 
its metallic state. 



ORGANIC COMPOUNDS. 103 

Calcium may be obtained for the purpose of vegeta- 
ble organization from a number of different compounds 
—common burned lime, chalk, marl, plaster, &c. Most 
soils are supplied with lime to some extent, and when 
there is a deficiency, materials are at hand and can 
easily be obtained by the agriculturist for remedying 
the defect. 

Of the remaining elements it is hardly necessary to 
speak again, as they usually occur in the soil in suf- 
cient quantity to supply the wants of vegetation. 

ORGANIC COMPOUNDS. 

From vegetable forms, a class of compounds may be 
obtained, quite unlike those which have been described. 
Starch, sugar, vinegar, &c., are produced by different 
processes trom vegetable substances, and are of very 
constant chemical composition. Of these the first two 
are composed of 12 atoms of carbon, 10 of hydrogen, 
and 10 of oxygen, and the compounds are expressed by 
the formula C12 Hi Oi 0. The constitution of vine- 
.gar, or acetic acid is indicated by the formula C 4 Ha O3. 
They are constituted of definite proportions of the dif- 
ferent elements, and have received the name of organic 
compounds. There is a great number of these, some 
derived from vegetable and some from animal substan- 
ces. They seem to be originated by the vital forces 
that produce the organization of animal and vegetable 
forms, and very few of them can be produced by the 
chemist by the union of the elements of which they are 
composed ; some of the compounds heretofore described 
are by some, ranked among organic compounds. 

It is exceedingly difficult to point out distinctly, the 
difference between organic and inorganic forms, but a 

Mention some organic compounds 1 What is their constitution ! 



104 AGRICULTURAL CHEMISTRY. 

few characteristics of the former will be given, which 
will form something of a line of division between the 
two classes. 

1. Organic compounds are remarkable for the com- 
plexity of their atomic constitution. The elements of 
which they are composed are quite limited in number ; 
most vegetable organic bodies being made up of carbon, 
oxygen, and hydrogen, those of animal origin contain 
nitrogen also ; but the number of atoms combined in 
these bodies is very great. 

2. By the application of heat these substances are 
charred and eventually decomposed. 

3. They are exceedingly prone to decomposition 
even by ordinary exposure to air and moisture. 

A description of the properties of a few of these sub- 
stances is here given, since they will be mentioned oc- 
casionally in the succeeding pages. Some of them are 
supposed to exert a favorable influence upon vegeta- 
tion, whilst others are apparently injurious. 

HUMUS. 

A brown substance consisting of carbon, oxygen, and 
hydrogen, is produced by the decay of vegetable sub- 
stances in the soil and is called humus. In the process 
of decay vegetable matter is continually changing its 
chemical composition ; oxygen is slowly absorbed from 
the air and the changes that ensue produce carbonic 
acid and water, the former being formed by the union 
of the carbon and oxygen of the plant, the latter by the 
combination of the oxygen of the air with the hydrogen 
of the decomposing substance. 

The result of this gradual change is, that a large 

What are the characteristics of organic compounds? What is the 
composition of humus '? W hat changes occur in the decay of vegetable 
matter 1 What compounds are formed ? , 



HUMUS. 



105 



number of compounds are formed, possessing the same 
elements and somewhat similar properties, but differing 
in the proportion in which those elements occur. Geine, 
ulmin, humic acid, humin^ &c., are different names ap- 
plied to the varieties thus produced, but they may all be 
considered as modifications of Awmz^s. The difference 
of composition is probably in some cases owing to the 
kind of vegetable from which the substance is obtained. 

The term vegetable mould as used by farmers, may 
apply to the different forms of humus as they occur in 
the soil mixed with inorganic matters. A part of the 
humus is soluble in alkalies, and may be obtained from 
most soils by the following process. First wash the 
soil and then boil it in a solution of ine carbonate of 
soda or potash in water : a colored fluid will be obtain- 
ed from which soluble humus, or humic acid, may be 
obtained by adding muriatic acid. It will be precipi- 
tated in the form of a dark flocculent substance, very 
slightly soluble in water. This process does not dis- 
solve the whole of the vegetable mould, and the re- 
maining mass contains a variety of humus sometimes 
called insoluble geine. Different terms, however, are 
used by different authors. " The modifications of hu- 
mus w*hich are soluble in alkalies, are called humic 
acid; while those which are insoluble have received 
the designations of humin and coal of humus. ^^ (Lie big.) 

Soluble humus forms compounds with the potash, 
soda, lime, &c. of the soil, and may be taken up by the 
roots of the plant, but with respect to the influence 
which these combinations exert upon vegetation, there 
is a wide difference of opinion. Some maintain that 
humus or its compounds taken up by the roots yields its 
carbon to the plant, and thus becomes an all important 

By what different names are they called? What is said of the term 
vegetable mould ? How is soluble humus obtained ? Describe it. To 
what compound is the term humic acid applied and to what humin 1 



106 



AGRICULTURAL CHEMISTRY. 



source of nourishment. Others deny that any favorable 
effect is produced by the humus contained in the soil. 
Liebig shows pretty conclusively that plants can not 
obtain iheir carbon from humic acid or its compounds. 
The follov^^ing are his reasons in a condensed form. 

"The opinion that the substance called humus is ex- 
tracted from the soil by the roots of plants, and that the 
carbon entering into its composition serves in some form 
or other to nourish their tissues, is so general and so 
firmly established, that hitherto any new argument in 
favor has been considered unnecessary ; the obvious 
difference in the growth of plants according to the 
known abundance or scarcity of humus in the soil, 
seemed to aftord incontestable proof of its correctness. 
Yet, this position, when submitted to a strict examina- 
tion, is found to be untenable, and it becomes evident 
from most conclusive proofs that humus in the form in 
which it exists in the soil, does not yield the smallest 
nourishment to plants. 

Vegetable physiologists agree in the supposition that 
by the aid of water, humus is rendered capable of being 
absorbed by the roots of plants. But according to the 
observation of chemists, humic acid is soluble only 
when newly precipitated, and becomes completely in- 
soluble when dried in the air, or when exposed in the 
moist state to the freezing temperature. 

Both the cold of winter and the heat of summer 
therefore are destructive of the solubility of humic acid, 
and at the same time of its capability of being assimila- 
ted by plants, so that, if it is absorbed by plants, it must 
be in some altered form. Facts, which show that hu- 
mic acid in its unaltered condition can not serve for the 
nourishment of plants, have not escaped the notice of 
physiologists ; and hence they have assumed that the 

What difference of opinion is mentioned ? Give Liebig's view. What 
does he say of the solubility of humic acid ? 



HUMUS. 107 

lime or the difFerent alkalies found in the ashes of veg- 
etables, render soluble the humic acid and fit it for the 
process of assimulation. 

Alkalies and alkaline earths do exist in the difFerent 
kinds of soil, in sufficient quantity to form such soluble 
compounds with the humic acid. 

Now, let us suppose that humic acid is absorbed by- 
plants in the form of that salt which contains the largest 
proportion of humic acid, namely in the form of hu- 
mate of lime, and then from the known quantity of the 
alkaline bases contained in the ashes of plants, let us 
calculate the amount of humic acid which might be as- 
similated in this manner. Let us admit likewise, that 
potash, soda, and the oxides of iron and manganese have 
the same capacity of" saturation, as lime with respect to 
humic acid. 

40,000 square feet of woodland yield annually, ac- 
cording to Dr. Heyer, on an average, 2,650 lbs. of dry 
fir wood, which contain 56 lbs. of metallic oxides. 

Now, according to the estimates of Malaguti and 
Sprengel, 1 lb. of lime combines chemically with 10'9 
lbs. of humic acid, which, admitting humic acid to con- 
tain 58 per cent, of carbon, would correspond to 91 lbs. 
of dry-wood. But we have seen that 2,650 lbs. of fir 
wood are really produced." 

The inference from this estimate is, that if all the 
potash, soda, lime, magnesia, iron, and manganese, con- 
tained in the fir-tree is taken up in combmation with 
humic acid, the amount of carbon supplied in this way 
would be very small compared with the amount really 
existing in the tree, — only about 2V of the whole. 

By another estimate, the same author shows that if 
all the rain water which falls during the summer 
months, should enter the plant, having in solution as 

According to his estimate what portion of the carbon of the plant may 
possibly be supplied by humic acid ? 



108 AGRICULTURAL CHEMISTRY. 

much as can be dissolved by it of the humate of lime 
(the most soluble of the humates ;) but a small portion 
of humic acid would be received, and a very insufficient 
quantity of carbon assimulated. 

It must not be inferred hovv^everthatLeibig supposes 
humus unimportant or ot little consequence as a fertil- 
izer. His argument is given to show that the absorp- 
tion of humic acid by the plant, either combined or un- 
combined would not supply the requisite amount of car- 
bon to the plant, but it is admitted that humus is a 
source from which this important element is derived. 
The following is his language on this point. 

" Humus acts in the same manner in a soil permeable 
to air as in the air itself; it is a continued source of carbon- 
ic acid, which it emits very slowly. An atmosphere of 
carbonic acid, formed at the expense of the oxygen of the 
air surrounds every particle of decaying humus. The 
cultivation of land, by tilling and loosening the soil, caus- 
es a free and unobstructed access of air. An atmosphere 
of carbonic acid is, therefore contained in every fertile 
sail, and is the first and most important food for the 
young plants which grow in it." 

Although it is evident that soils are most productive 
which contain a proportion of vegetable mould, yet it 
is no less certain that vegetable forms whether plants 
cultivated for food, or forest trees, derive their carbon 
mostly from the air. It is certain too that large crops 
are often obtained from soils containing very little hu- 
mus or carbonaceous matter in any form. 

What then, is the function of humus in the great pro- 
cess of vegetable organization ? Is its presence neces- 
sary in order to provide carbon for the plant. ? 

What other estimate by the same author 1 Does Leibig suppose hu- 
mus of no avail? What does his argument show? How does he say 
that humus acts 1 From what source do plants mostly derive their car- 
bon ? 



OXALIC ACID. 100 

It is not absolutely required for the purpose of sup- 
plying carbon, after the plant has appeared above the 
ground and opened its leaves to the air, for it is princi- 
pally through the leaves that the carbonic acid of the 
air is taken up ; but before the tender shoot is supplied 
with exterior organs, and while its roots are the only 
absorbents of carbonic acid, humus in process of de- 
composition doubtless supplies nourishment, 

OXALIC ACID. 
C2 03=36. 

This acid is found in certain plants, generally in com- 
bination with potash or lime. It is a transparent crys- 
taline substance, sour to the taste, and poisonous. It is 
not only destructive of animal life, but is prejudicial to 
most vegetable forms which are cultivated for food. 

Oxalic acid may be formed artificially by the action 
of nitric acid upon starch. It unites freely with lime, 
potash, soda and other bases ; the oxalate of lime is 
totally insoluble in water, and therefore, when oxalic 
acid occurs in the soil, it can be rendered harmless by 
the application of lime. The presence of sorrel upon a 
piece of ground indicates the existence of this acid in 
quantities hurtful to vegetation, and lime should be im- 
mediately applied to neutralize it. 

From sorrel is obtained the oxalate of potash which 
from its origin is called salt of sorrel. 

Under what circumstances does humic acid supply nourishment to the 
plant ? What is the composition of oxalic acid ] Describe it. How 
may it be formed artificially ? What does the presence of sorrel on a 
soil indicate ? How may the oxalic acid be neutralized ? What salt is 
obtained from sorrel ? 



110 AGRICULTURAL CHEMISTRY. 



ACETIC ACID, OR VINEGAR. 

Common vinegar is a very dilute and impure form 
of acetic acid, but can be freed from its impurities by 
distillation. This acid occurs in the juices of many 
plants, and may be obtained from common Vi^ood by 
exposing this to a high heat in an iron retort ; the acid 
distils over and by means of a condensing apparatus is 
collected, but in an impure state ; certain oily and tarry 
substances are produced by the same process, and must 
be separated from the acetous liquor. 

A large number of organic compounds are formed in 
the plant, and may be separated from them by different 
processes, but it will not be profitable to go into an ex- 
amination of them here ; we hence close the considera- 
tion of those substances which constitute the plant and 
examine thefo7xes or agents which produce the requi- 
site combinations in the organization of vegetable 
forms. 

What is common vinegar? How is acetic acid obtained from woodi 



PART IV. 

CHEMICAL FORCES, 



We have seen that there is in nature a limited num- 
ber of elementary forms, and that these elements unite 
with each other, producing an almost infinite variety of 
compounds. 

Now as no effect is without a cause, and no change 
produced except by some active force, it follows that 
certain agencies must be in action that cause the union 
of elements or compounds with each other, or separate 
them when united. The chemical forces are attraction, 
heat, light, and electricity. The phenomena connected 
with the manifestations of these different forces, are|in 
some points similar, and it is possible that after investi- 
gation may prove the identity of different forces, indeed 
they may all prove to be modifications of one univer- 
sal, all-pervading agent. 

ATTRACTION. 

This agent will be examined under four different 
modifications, gravitation, cohesion, capillary attraction, 
and chemical affinity. The first three do not have a 
direct bearing upon this department of science, but are 
incidentally connected with it, 

Gravitative attraction is an all prevading property 
of matter, we see its effect not only in the fall of the 
acorn from the oak, or the destructive descent of the 
avalanche from its dizzy height, but in the descent of 

What forces produce chemical changes? Give three kinds of attrac- 
ition mentioned. 



112 AGRICULTURAL CHEMISTRY. 

the smoke towards the earth, and the lowering of the 
clouds when their density is increased. The effect of 
gravity is not only to make things gravitate towards 
the earth, but in an equal degree proportionally, to make 
them gravitate towards each other. 

Two balls suspended by cords at a short distance 
from each other, have not only a tendency towards the 
earth, but towards their own centres. 

All have observed that different bodies move towards 
the earth with different forces, and if we were asked 
why this was so, we might perhaps answer " because 
some bodies weigh more than others," forgetting that 
what we term weight is only the gravitating force of the 
substance which we weigh. This force depends upon 
the quantity of matter contained in the substance. A 
cubic inch of lead will gravitate towards the earth with 
ten times the force of a cubic inch of cork, because 
the former contains ten times as much matter as the lat- 
ter. In ascertaining the weight of bodies it becomes 
necessary to have some standard of comparison ; water 
has been assumed as that standard, the weight of 
27*72 cubic inches being called a pound ; for the sake 
of convenience, we have substituted metallic weights 
instead of water. 

By the specific gravity of any substance we mean 
its weight compared with the weight of the same bulk 
of water; let us suppose for illustration that a cubic inch 
of iron weighs 8 times as much as a cubic inch of water, 
or we will suppose that by weighmg a cubic inch of 
iron we ascertain that it balances 2016 grains, and the 
same bulk of water, 252 grains. Now since the spe- 
cific gravities of the two will be in proportion to their 

What is the effect of gravity 1 What is weight ? Why does lead 
weigh more than cork % What is the standard of comparison in ascer- 
taining the weights of bodies? Explain what is meant hy specific grav- 
ity. What ilhistration is given 1 



ATTRACTION. 1J3 

weights, if we assume 1 as the number to represent the 
specific gravity of water, we shall have the following 
proportion, 252: 2016:: 1:8. 

Giving 8 for the specific gravity of iron. But it would 
be inconvenient and almost impossible to give to the dif- 
ferent substances, whose specific gravities we wish to as- 
certain, the form of cubes, and hence it is necessary to 
adopt some other method by which we can ascertain, 
the specific gravities of bodies of irregular forms. If 
we can ascertain the weight of a portion of water of 
the same bulk as the irregular solid, we have sufficient 
data from which to determine the specific gravity. 

If we have a rough mass of iron weighing 96 ounces, 
and by some means we discover that a portion of water 
of the same bulk weighs 12 oz. we should then obtain 
the specific gravity as before. 

The following is the method by which we ascertain 
the weight of a bulk of water equivalent to that of any 
substance heavier than water. 

If an irregular mass of marble be suspended in a 
tumbler even full of water a quantity of the fluid wilt 
be displaced just equal in bulk to the substance and the 
weight of that amount of water will be indicated by 
the loss sustained by weighing the article in water. 

Then if a substance weighs 480 grains in the air and 
only 400 in water, 80 the loss, will indicate the number 
of grains which the same bulk of water weighs, and 
the proportion 80: 480:: 1, gives 6 the specific gravity. 
It will be noticed that 1 is always the third term, there- 
fore the whole operation consists in dividing the second 
term by the first. Then the following steps are all that 
are necessary. 

What number represents the specific gravity of water? How can we 
ascertain the weight of water of the same bulk as any given solid heav- 
ier than water 1 Give an illustration. 

*2 



114 AGRICULTURAL CHEMISTRY. 

1. Weigh carefully and note the number of grains or 
ounces. 

2. Weigh in water and subtract from the first weight. 

3. Divide the weight in air by the difference of the 
two weights, and the quotient will be the specific grav- 
ity. 

Example, A mineral weighs 525 grains in the air, 
and 500 grains in water ; what is its specific gravity '.' 

To determine the specific gravity of soils, take a 
bottle with a small neck and fill to a certain point in the 
neck with water, and mark the point with a file ; empty 
a part of the water and introduce a weighed portion of 
the soil ; after it is well mixed with the water, bring the 
fluid to the marked point and weigh again. The last 
weight will evidently be the greater, and the difference 
will arise from the diflference of the weight of so much 
soil, and a similar bulk of water. This diflference 
subtracted from the weight of the soil will give that 
of a similar bulk of water. Then divide the weight of 
the soil by this last difference, and the quotient will give 
the specific gravity. 

To obtain the specific gravity of liquids, take a bottle 
of the same kind used to obtain the specific gravity of 
soils ; introduce 1000 grains of water and mark the point 
to which the water rises on the neck, fill to the same point 
with the fluid whose specific gravity is to be ascertained 
and weigh ; the weight will be the specific gravity 
considering 1000 as that of water. 

Example, if alcohol be introduced into the bottle, 
and is found to weigh 912 grains, then 912 will 
be the specific gravity of alcohol, water being 1000, 
or -912, water being 1. 

Give the three steps for ascertaining the specific gravity ? How do 
we ascertain the specific gravity of soils ? Of liquids ? 



COHESIVE ATTRACTION. 115 



COHESIVE ATTRACTION. 

This kind of attraction seems to act only when the 
particles of matter which it influences are apparently 
in contact. Hence it has been said to act at insensible 
distances, or at distances so small that they are inap- 
preciable. It is well known that if a piece of wood be 
once split, the parts cannot be made to cohere again, 
although pressed together with considerable force, 
without the intervention of some other substance. It 
is because the particles are not brought into sufficiently 
close contact to induce cohesive attraction. There are 
solids however, which after being divided may be made 
to unite again by pressure. 

If a lead ball be divided in the centre and both sur- 
faces made perfectly smooth and bright, they can be 
made to unite by pressing the portions together with a 
twisting motion, the portions will adhere with considera- 
ble tenacitv. 

Two pieces of polished plate glass, are sometimes 
united by pressing their smooth surfaces together, and 
often so perfect is the union they can not be separated, 
but will be fractured at other points sooner than part 
at the points of union. 

So long as two pieces of lead or glass, in the condi- 
tion referred to, are separated by the least perceptible 
space, this attractive force is not exerted. Newton 
supposed that this attraction was limited to the distance 
of less than the millionth part of an inch, thus we see 
that whilst gravitative attraction acts at all distances, 
cohesion is confined to very narrow fimits. 

When does cohesion act % Why can not pieces of wood that have 
been separated, be made to re-unite by pressure ? What illustrations is 
given of the cohesion of tvsro pieces of lead 1 Give the experiment^ with 
two polished plates of glass. To what distance is the attraction of 
cohesion limited 1 



116 AGRICULTURAL CHEMISTRY. 

The intimate connection of the subject of cohesion 
and heat, renders it necessary to defer the farther con- 
sideration of this subject, until we treat of that agent. 

CAPILLARY ATTRACTION. 

It is this kind of attraction which causes fluids to rise 
above their natural level in tubes of small calibre, and 
derives its name from a latin word, which signifies hair^ 
because the tubes have a hair-like bore. It is this kind 
of attraction that causes the sponge to absorb water. 

In the vegetable world, we see the action of this prin- 
ciple in the absorption of the fluids of the earth by the 
plant. Most of the elements of which plants are com- 
posed, are obtained in this manner; being soluble in 
water they are taken up with it and are retained to 
form part of the plant. The body of every tree is noth- 
ing but a map of capillary tubes, and so of every limb 
and leaf. What is called ihe sap of the tree is the fluid 
drawn from the earth ; this ascends to the leaves and 
then again descends through the bark to the earth, 
having parted with that which was necessary to the 
growth of the tree. This process, however, can not be 
sufficiently explained by saying that it is the effect ot 
capillary attraction. 

If a capillary tube be placed with one end in water, 
and the fluid be raised one inch above its natural level 
by lowering the tube gradually until less than an inch 
of the upper end is left above the surface of the water,, 
it will be seen that the water will not run over the top 
of the tube. This experiment shows that capillary tubes 
will not raise water above their own extremities ; yet, 
if we cut off" the top of a vine when full of sap, the fluid 

In what respect do gravity and cohesion difler 1 What is capillary 
attraction 1 What causes water to rise in the sponge 1 What is said 
of the body of every tree ? Will capillary tubes raise water abeve their 
QVfn extremities ? 



CAPILLARY ATTRACTION. Ill7 

will run over the top of it, proving that something be- 
sides mere capillary attractions causes the sap to ascend 
the plant. 

The toUowing expermient by Draper illustrates this 
point. 

" In the month of April, 1834, 1 cut a vine, which was 
growing wild on the edge of a forest in Virginia, asun- 
der with one blow of an axe ; the cut surface which 
was one and a half inch in diameter, exhibited its open 
vessels from which there poured out an uninterrupted 
stream of ascending sap. In the course of eight hours 
there was collected of this fluid seventy ounces, and 
this was probably a far less quantity than would have 
been raised under ordinary circumstances when the 
leaves aided the spongioles by their exhausting and 
pushing aclion." 

Another experiment of a different character will tend 
to explain this cause of the flow of sap above the level 
to which it would be carried by capillary attraction 
alone. " If one end of an open glass tube be covered 
with a piece of moistened bladder or other fine animal 
membrane, tied tightly over it and a strong solution of 
sugar in water be then poured into the open end of the 
tube so as to cover the membrane to the depth of sev- 
eral inches, and if the closed end be then introduced to 
the depth of an inch below the surface of a vessel of 
pure water, the water will after a short time pass through 
the bladder inwards and the column of liquid in the tube 
will increase in height. This ascent will continue till, 
in favorable circumstances, the fluid will reach the 
height of several feet and will flow out or run over at 
the end of the tube. At the same time the water in 
the vessel will become sweet, indicating that while so 
much liquid has passed through the membrane inwards, 
a quantity has always passed outwards carrying sugar 

Relate the experiment of Draper. Experiment by Johnston. 



118 AGRICULTURAL CHEMISTRY. 

along with it. Instead of sugar, common salt gum, or 
other soluble substances may be dissolved in the-water, 
and the denser this solution, the larger the quantity of 
water that will enter by the membrane, and the great- 
er the height to which the column will rise. 

These appearances bear a strong resemblance to 
those presented in the absorption and excration of fluids 
by the roots of plants. Thus, if the spongy termina- 
tion of the root represents their porous membrane in 
the above experiment— the sap with which the tubes of 
wood are filled, the artificial solution introduced into the 
experimental tubes and the water in the soil, the fluid 
into which the closed extremity of the tube is introdu- 
ced, we have a series of conditions precisely like those 
in the experiment. Fluids ought, consequently, to enter 
from the soil into the roots, and thence to ascend the 
stem, as in nature they appear to do." (Johnston.) 

The cause of this ascent of fluids, both in the tree 
and in the experimental tube are supposed to be due to 
the action of two opposite currents of electricity, and 
in treating of that agent we shall refer to its action in 
causing the circulation of the sap. 

The eflfect of capillary tubes upon fluids, depends 
upon the power of the latter to wet the surface of the 
tubes ; consequently those fluids that do not wet the 
tube, are not raised by it above their ordinary level, 
but perhaps are depressed ; this result follows when a 
glass capillary tube is plunged into a vessel of mercury. 
The mercury has no affinity for the glass and is not 
elevated by it. Water, on the same principle, is not 
raised by a tube having its inner surface coated with 
oil. We infer then that capillary attraction is caused 
by the affinity of the sides of the tube for the liquid 
which is raised. 

In what respect is the plant like the experimental tube ? To what is 
the circulation of the fluids owing? On what does the power of capillary 
tube to raise a fluid depend 1 Are fluids raised that do not wet tne tubes ? 



CHEMICAL AFFINITY. 119 



CHEMICAL AFFINITY. 



Chemical attraction, otherwise called chemical affin- 
ity, is that which causes substances of different kinds to 
unite and form new compounds, different from the sub- 
stances united. For instance take a solution of chloride 
of calcium and unite with it a portion of oil of vitriol, 
(sulphuric acid.) The two liquids rapidly unite and 
form a white solid, familiar to all under the name of 
plaster of Paris. 

It will be well here to mark the changes that are 
produced in this experiment. The composition of the 
acid is represented by the formula SO 3, and that of the 
chloride of calcium CI Ca and water, (H O,) is com- 
bined with each when in a fluid state. The sulphuric 
acid has a strong affiniti/ for lime, (CaO,) therefore cal- 
cium unites with oxygen for which it has an affinity, 
and the acid and base then unite to form plaster, (sul- 
phate of lime ) The calcium obtains its oxygen from 
the water, and the hydrogen released by the process, 
unites with the chlorine, forming muriatic acid (hydro- 
choloric acid.) 

In this experiment we have an illustration of one of 
the effects of affinity, a solid produced by the union of 
two liquids : another effect is, the formation of a solid 
by the union of two gases, as in the process for form- 
ing carbonate of ammonia, (page 66.) 

By the action of the same force two substances can 
be united which burst into a flame at the moment of 
their union, so great is the heat caused by their combi- 
nation. 

What is chemical affinity ? What is the first illustration of its effect ? 
Describe the changes that occur in this experiment. What results from 
the union of carbonic acid gas and ammonia 1 




120 AGRICULTURAL CHEMISTRY. 

An experiment of this kind is represen- Fig. 16. 
ted by Fig .16, in which the metal potassium 
has such an affinity for oxygen that it de- 
composes water for the sake of obtaining it, 
and the heat produced by the combination 
is sufficient to inflame both the hydrogen 
and the metal. The hydrogen in burning unites with 
the oxygen of the air, and thus as much water is re- 
produced as is decomposed by the metal. 

Oxygen appears to have the greatest range of affin- 
ities of all the elements, combining with most of its 
fellows, and often with a single one, forming a number 
of different compounds. It is on account of the affini- 
ty of oxygen for iron, that water is decomposed, and 
hydrogen released, in the process given on page 22 ; 
the oxygen of the vapor of w^ater unites with the red 
hot iron wire in the tube. 

Fig- 17. In the production of hydrogen by the action of 
dilute oil of vitriol upon zinc, as represented in 
Fig. (17,) the affinity of oxygen for the zinc, caus- 
es the union of the two and the water is thus de- 
composed. The sulphuric acid from its affinity 
for the oxide of zinc dissolves it as it is formed, and 
thus a fresh surface of the metal is continually 
presented to the oxygen. The only object of the 
acid is to prevent an accumulation of the oxide upon 
the surface, as that would put an end to the process of 
decomposition. 

What changes does affinity produce when potassium is poured upon . 
water ? What is said of the affinity of oxygen for different elements ? 
Why is hydrogen released in the process given on page 27? Explain 
ihfi changes connected with the production of hydrogen by the procew 
represented in fig. 17. 



HEAT. 121 



HEAT. 



This is an all important agent in the production of 
those changes that are continually occurring around us. 
The first effect of heat is to expand bodies or separate 
Iheir particles farther and farther from each other. We 
have before alluded to the intimate connection of the 
subject of cohesion with that of heat. 

It will be seen at once that if heat has a tendency to re- 
move the particles of matter from each other, it must 
in a similar degree overcome the attraction of the par- 
ticles for each other, and since these forces are contin,- 
ually in operation, the one tending to hold together, and 
the other to separate the atoms of solids, it follows that 
cohesion and heat may properly be called antagonistic 
forces, ever opposed and each striving for the mastery. 
As heat is gradually withdrawn from a body, the atoms 
of which it is composed are drawn nearer and nearer 
together by the force of cohesion, yet are never made to 
touch each other. On the contrary, when heat is ap- 
plied, the spaces by which the atoms are separated 
become larger, and if the cohesive force is sufficiently 
counteracted, the particles of matter of which it is com- 
posed will move freely among each other, and the solid 
will be changed to a liquid. If a still higher degree of 
heat be applied the particles seem to lose almost whol- 
ly the principle of attraction, and the fluid is changed 
to an invisible vapor. If a piece of zinc be gradually 
heated, the first effect will be to expand it ; it will next 
become liquid, and eventually be changed to vapor. 

Heat has much to do with the changes going on in 
the vegetable world ; indeed all are so familiar with its 
influence upon vegetation that it seems hardly necessa- 
ly to enlarge upon it. It is well known that the growth 

W^hat is the first effect of heat 1 What is said of the relation of co- 
hesion and heat to each other ? What effect is produced by withdrawing 
heat from a body 1 



122 AGRICULTURAL GHEMISTRT. 

of particular plants depends upon the temperature of 
the region. Wheat and barley will not flourish in the 
northern hemisphere farther south than the 20® of north 
latitude. The northern limit for wheat is 64®, of barley 
80®. Height above the sea produces the same effect 
as a change of latitude, a height of 600 feet being 
equivalent to a change of 1® of latitude. 

Some degree of heat is necessary to produce germi- 
nation of seeds, and after this to expand the cells and 
pores of the plant, so as to facilitate the circulation of 
the sap. 

The son is the great source of heat. By this the 
earth is warmed during the day, and as all bodies are 
continually radiating their heat and imparting it to 
cooler bodies around them, in the absence of the sun 
the earth loses by radiation a large quantity of heat, 
and the temperature becomes much lower ; the air lying 
near the surface is cooled by contact and the vapor 
floating in it is condensed and assumes the form of 
water, this deposit is denominated dew. If the air be 
sufficiently cold, this vapor will be deposited in the form 
of minute particles of ice and is then denominated/ro^i. 
The cause then of dew and frost is found in the rapid 
radiation of heat from the earth into space in the absence 
of the sun. Now since all bodies radiate heat to those 
around them, it follows that when a mass of clouds are 
lying above a portion of the earth, they will radiate 
heat in return, and thus the temperature of the earth 
remaining the same or nearly so, the phenomena of 
dew and frost do not appear. If frost occurs while the 
plants are young and tender, it proves a very destruc- 
tive agent. Its first injurious effect is produced by 
freezing the sap of the young plant, and as this must 

State the effect of the sun upon the earth? What occurs in the ab- 
sence of the sun ? Explain the phenomena of dew and frost 1 How- 
does a canopy of clouds prevent dew and frost 1 What is the effect of 
frost upon plants ? 



HEAT, 123 

expands while freezing, the pores of the plant would 
necessarily be distended and perhaps lacerated. Yet 
it is contended by some that the freezing of the plant 
will not injure it, if it is thawed with sufficient care. — 
The following is a statement of their views. 

" The reason why potatoes, apples, &c., become soft, 
and rot when frozen and then suddenly thawed, uncov- 
ered and in the open air, is the sudden thawing. You 
may put a heap of apples on the floor of a room, or 
other dry place, where they will freeze perfectly hard, 
and if covered close with anything that will exclude 
the air, when the weather becomes warm enough to 
thaw, the apples will remain sound and uninjured, after 
they are thus closely thawed. The cover may be of 
coarse tow of flax, or any article that will cover them 
so as to exclude the air. They may be suffered to re- 
main so in a garret or any dry place, where it freezes 
hard and they will be found sound and free from injury, 
if the barrel remains tight till they are thoroughly 
thawed. It is the sudden thawing that causes the ap- 
ples or other vegetables to become soft and rot. So 
if the fingers of your hand be frozen, and you expose 
them to sudden heat by warming them at the fire, and 
they suddenly thaw, the flesh will mortify and slough 
oflf; but if you freeze your fingers or other limbs, and 
put them in snow and rub gently till they thaw, or put 
into a pail of water just drawn from the well, which 
will be less cold than your frozen fingers — they will 
thaw slowly and suffer but little injury. So during the 
early autumnal frosts in September, if the morning after 
the frost is cloudy, the frost will be drawn slowly from 
the frozen vegetables, and they will be uninjured ; but if 
they receive the rays of the early and clear sun, they thaw 
so suddenly, that they will hang their heads and perish. 

What is supposed by some ? Illustrate. What is said of a frozen 
hand 1 What is the effect of a cloudy morning after a heavy frost ? The 
effect of a clear morning? 



124 AGRICULTURAL CHEMISTRY. 

If wet with water from the well long enough to extract 
the frost before the sun shines on them, they do not suf- 
fer." (Cultivator.) 

The following reasons, given by Johnston, show why 
the thawing and not the freezing of plants is the cause of 
their destruction. " When the plant freezes, the fluid por- 
tions slightly expand in becoming solid, but the air in the 
air vessels contracts in at least an equal degree, and thus 
allows a lateral expansion of the sap vessels sufficient 
to prevent injury. When the temperature is shghtly 
raised the air expands but slightly and ice is melted 
long before the gaseous substances reach their original 
bulk. But if the rays of the sun strike suddenly upon 
the leaf, the surface may at once be raised in tempera- 
ture 80 or 40 degrees. The air will expand suddenly, 
and before the sap is thawed may have distended and 
torn the vessels, and cause the sap and air to be mutu- 
ally intermingled, chemical changes will immediately 
ensue, and the plant will decay." 

We see then that if we would prevent the frost from 
accumulating upon plants, we can accomplish it by 
throwing over them a covering which shall operate like 
the clouds in a cold night in preventing it. Jf they have 
already become frozen, protect them from the rays of 
the approaching sun, by means of a similar covering, 
or by throwing cold water upon them, that they may 
not be suddenly thawed. 

Notwithstanding the evil efl^ects of frost, it is under 
other circumstances highly beneficial. It breaks up and 
finely pulverizes the soil during the winter months, and 
does it more thoroughly than could be accomplished by 
mechanical means. This pulverization is not accom- 
plished during a mild winter, and there is a failure of 

How may this be prevented ] What explanation is given by Johns- 
ton? How should frozen plants be protected"? In what way does frost 
act beneficially ? 



HEAT. 125 

crops in consequence. The effect of frost is most ob- 
vious upon stiff clay soils, they should therefore be 
ploughed in the autumn or beginning of winter. 

Combustion is also a source of heat. Many experi- 
ments have been described in which the union of oxygen 
with different substances has produced both light and 
heat, and it has been shown that all ordinary cases of 
combustion result from the union of oxygen with the 
burning body, hence it would be a natural inference, 
that combustion is produced by the union of oxygen 
with a body with sufficient rapidity to produce light 
and heat. This perhaps is the sense in which the term 
is generally used, but in a strictly chemical sense the 
definition is not broad enough, for light and heat are 
produced by combinations in which oxygen takes no 
part. Sulphur and iron will combine, under certain 
circumstances, and both heat and light accompany the 
combination : thus iron wire may be burned in a jet of 
the vapor of sulphur issuing frorn an apertur€ in a red 
hot gun barrel, but no oxygen unites with the burning 
body. 

Combustion accompanies the union of phosphorus 
and iodine, for by percussion a mixture of the two is 
caused to hurst into a flame. 

Combustion then is the evolution of heat and light 
produced by the combination of different chemical sub- 
stances. Condensation is sometimes given as a source 
oi heat, but if we carefully consider ihe phenomena of 
combustion, it will be seen that they imply the process 
of condensation, for in all cases the result of combus- 
tion is a body either solid or otherwise, more dense 
than the substances united, that is, occupying less 
space than that occupied by the two before combustion. 

Where are its effects most obvious? What other source of heat is 
mentioned? From what do all ordinary cases of combustion result ? 
Are light and heat produced by combinations in which oxygen takes no 
part ? Illustrate. 
♦2 



226 



AGRICULTURAL CHEMISTRY. 




In the combination of oxygen with carbon, producing 
carbonic acid, as in the combustion of charcoal in air 
or oxygen, the resuhing gas, consisting of two propor- 
tions of oxygen and one of carbon, fills only the space 
before occupied by the oxygen alone, the two elements, 
therefore, have been condensed in the act of combining : 
the space before occupied by 11 grains of oxygen, 
contains after combustion, 15 grains of carbonic acid. 
Fig. 18. In the ignition of iron wire in oxygen gas, all 
the oxygen unites with the iron, and many cubic 
inches of the gas, are condensed in each of the 
1 melted globules that fall from the wire ; here we 
I see the reason why so great a degree of heat is 
produced in this experiment, the intensity of the 
heat is proportioned to the rapidity and extent 
of the condensation. A similar result is produced in 
the combustion of phosphorus in oxygen ; a large vol- 
ume of gas and a portion of phosphorus are condensed 
in a small quantity of phosphoric acid. 

In the production of musical tones as rep- 
resented in (Fig. 19.) the hydrogen generated 
in the bottle and burned at the end of the tube, 
unites with the oxygen of the air, and produ- 
ces water: this will be indicated by the accu- 
mulation of vapor on the inner surface of the 
tube. Here we have a great degree of heat, 
produced by the rapid conversion of two 
gases' into a liquid. 

If oxygen and hydrogen be conveyed by 
separate tubes to a common jet, and the mix- 
ture inflamed, the combination of the gases, produces a 




Give the definition of comhustion ? What is the result of ordinary 
combustion 1 The space occupied by 11 grains of oxygen before com- 
hastion, contains how many of carbonic acid afterwards ? What degree 
of condensation occurs in the comhustion of iron in oxygen? What is 
4he cause of the heat in the experiment represented in Fig. 19? 



HEAT. 127 

most intense heat. The apparatus arranged for this 
purpose is called a compomid blowpipe, and by means 
of it the most refractory substances are fused. Platinum, 
silica, and other substances that are utterly infusible in 
any furnace, are readily melted in the oxyhydrogen flame. 
In this experiment, as in the last, the intensity of the 
heat is owing to the amount of gaseous matter that is 
rapidly converted into water ; the effect is greater in 
the latter case because oxygen and hydrogen unite with 
greater rapidity than in the former ; in this union 2000 
cubic inches of the gases form but 1 cubic inch of 
water, and the combination is rapidly effected. 

We may state as a general principle, that a like 
degree of condensation ever produces a like degree of 
heat, that is, in the union of the same substances ; thus 
the formation of a certain amount of carbonic 
acid, by the union of carbon and oxygen, al- 
ways produces a fixed amount, of heat, and a 
pound of carbon, as we have already asserted, pro- 
duces the same degree of heat, when consumed in the 
process of respiration, as when burned in a coal fire ; 
the same condensation must take place, whether the 
union is accomplished in a longer or shorter space of 
time. The process by which the carbon of the blood 
is consumed, is strictly a kind of combustion^ although 
unaccompanied by any sensible light ; yet who can say 
that light is not produced. The slow combustion of 
phosphorus, as it occurs when that substance is ex- 
posed to the air, produces both heat and light, but the 
heat is not appreciable and the light is not seen in open 
day; yet this is plainly a process of combustion. 

In the spontaneous rusting of iron, there is as much 
oxygen condensed, as when the metal is burned in the 

Explain the principle upon which heat is produced by the compound 
blowpipe? What substances are fused by itl State the degree of con- 
densation produced. What general principle is stated ? "What is said 
of the heat produced by respiration 1 



128 AGRICULTURAL CHEMISTRY. 

pure gas. Does it not follow then, that just as much 
heat is produced in the former case as in the latter ? 
May we not even suppose the same degree of light to 
be really evolved in the rusting of iron as when it is 
brilliantly ignited in oxygen ? Light is often given out 
by bodies, when we do not perceive it. It has been 
seen radiating from the poles of a magnet ; not how- 
ever, by persons in health, but by individuals, afflicted 
by a certain disease that rendered the optic nerve re- 
markably sensitive, and enabled them to detect the 
presence of light where none could be perceived by 
others. 

We may safely conclude, that in all cases of com- 
bustion, there is a degree of condensation, commensu- 
rate with the heat produced, and that the same degree 
of condensation, in the union of any two substances is 
ever accompanied by the evolution of a like degree of 
heat and light. 

We have seen that the effect of caloric* is to remove 
the atoms of which bodies are composed, farther from 
each other, that is, the particles of matter, which are 
never in contact, make room, so to speak, for the heat 
which enters the body. If then in the act of expanding, 
bodies absorb heat, we should naturally expect, that 
whenever bodies by any means are rendered more 
dense, a certain amount of heat will be given out ; for 
their particles are by this means brought nearer each 
other and the heat must be expelled. This also may 
be observed, that, whenever bodies expand without the 
application of heat, there is still just as much heat taken 
up, as when it is directly applied. If ice be melted by 

* The terms heat and caloric are used synonymously. 

Is light often produced when we are not able to perceive it 1 What 
illustration is given ? What may we conclude with regard to all cases 
of combustion ? 



HEAT. 129 

uniting with it substances that have a great avidity for 
moisture, and without applying heat, there still will be 
as much caloric absorbed, as when the ice is melted 
over the fire, and this heat must be taken from sur- 
rounding objects. It is well known that common salt 
and pounded ice combined, form a freezing mixture^ 
and substances surrounding a vessel containing these, 
are solidified by the cold produced : this result is caused 
by the rapid liquifaction of the two solids without the 
application of heat. 

The heat that enters the ice and salt, is said to be 
latent, because the temperature of the mass is not raised 
until it has all become liquid, although caloric is rapidly 
absorbed every moment. A more striking instance of 
the effect of liquifaction is exhibited in the mixture of 
sulphate of soda (Glauber's salt) and muriatic acid, eight 
parts of the former to five of the latter ; the Glauber's 
salt immediately assuming the liquid form, a large quan- 
tity of caloric is absorbed from surrounding objects, and 
a sufficient degree of cold is produced to freeze water 
contained in a tube placed in the mixture. 

The amount of heat that becomes latent in such cases, 
depends upon the quantity of solid matter that is liqui- 
fied in a given time. 

If liquifaction necessarily implies the absorption of 
caloric, then must vaporization produce a similar effect, 
only in a greater degree, for when a liquid is converted 
into vapor, the particles become far removed from each 
other, and much heat must enter and exert its repulsive 
power in keeping the atoms apart. 

The most common illustration of this effect, is to pour 
alcohol or ether upon the hand and notice the cold pro- 

When bodies expand without the application of heat what follows 1 
Common salt and pounded ice form what? Why? What is said of the 
heat absorbed 1 Why? Give another method of forming a freezing 
mixture. Why is such a degree of cold produced ? What determines 
the amount of heat that becomes latent? 



130 AGRICULTURAL CHEMISTRY. 

duced by the rapid evaporation. If water be rapidly 
converted into vapor v^^ithout the application of heat, 
so much caloric will be rendered latent, that the water 
will be frozen. This may be illustrated by placing 
water under the receiver of, an air pump, in a vessel 
well coated with lamp-black, that caloric may not be 
conducted to the fluid ; by exhausting the receiver, a 
rapid evaporation takes place from the surface of the 
water, and the heat rendered latent being taken from 
the fluid, the latter is converted into ice. 

There are many interesting points connected with 
the phenomena of heat, upon which we can not dwell 
in a work thus limited in its nature. Of electricity as 
a source of heat, we shall speak when treating of that 
agent. 

ELECTRICITY. 

It was discovered by the ancients, that if amber w^as 
rubbed with woolen cloth, silk, or similar substances, it 
became possessed of the property of attraction, and light 
substances would adhere to it. This property, which 
is also capable of being induced in rosin, sealing wax, 
silk, &c., is owing to the presence of electricity. It is 
not necessary here to describe minutely all the phe- 
nomena connected with the manifestations of this force, 
and we will give merely an epitome of the most com- 
mon. 

If a dry and warm tube of glass be rubbed briskly 
with a silk handkerchief, and then be immediately 
presented to a pith ball, suspended by a silk thread, 
the ball will quickly attach itself to the tube, but 
in a short time will be thrown back, and the two 

What is the effect of converting a Hquid to vapor 1 Illustrate. State 
the effect of the rapid evaporation of water under the receiver of an air 
pump. State the effect produced by rubbing amber with silk. To what 
,is this effect owing ? 



ELECTRICITY. 131 

will mutually repel each other. In this experiment 
the pith ball becomes electrified or charged with elec- 
tricity. If two balls be thus effected they will repel 
each other, and will have the power of attracting sub- 
stances not electrified. If the pith balls be suspend- 
ed by wire, no matter how fine, they will not remain 
electrified except while connected with the tube. The 
glass rod, whilst excited, exhibits a phosphorescent glow 
in the dark, and if the electricity be differently accumu- 
lated, an electric spark will leap from the surface of the 
tube to the hand presented to it. If a rod of metal, in- 
stead of glass, be rubbed in the same way, no electrical 
effects will be produced. 

These are the principal phenomena connected with 
electricity ; attraction, repulsion, electrical light and 
the spark. 

To explain these we will suppose, in accordance with 
the theory of Dufay, that there are two kinds of elec- 
tricity, and bodies in their ordinary state, contain the 
two in a state of equilibrium, but by friction the equili- 
brium is destroyed in certain substances, such as glass, 
rosin, (fee, and an accumulation of one kind of electri- 
city or the other, is produced. By friction a glass 
tube becomes charged with a kind of electricity called 
vitreous, or positive, whilst rosin by the same means is 
thrown into a different state, and the electricity is called 
resinous or negative. If two pith balls be electrified, 
one by excited glass, the other by rosin, they will at- 
tract each other, but if both be charged from the same 
substance, they will mutually repel, as has been stated. 
From this experiment we draw the inference that bodies 
in the same electrical state repel, and those in different 
states attract each other. 

State the different phenomena exhibited by means of an excited tube. 
What is said of bodies in their ordinary state 7 



132 AGRIcr:.rURAL CHEMISTRY. 

We see by this why a light substance is first attract- 
ed to the excited tube and then repelled. Glass, rosin, 
and all those substances that can be excited in a simi- 
lar manner are called electrics ; the term non- electrics 
is applied to those substances, that can not be excited 
in a similar manner, although even these can be excited 
when properly arranged : the metals and many other 
substances belong to this class. 

When electricity accumulates upon the surface of an 
electric, it is retained and -not allowed to escape, al- 
though it has a great tendency to do so, the electrics 
are, therefore, called non-conductors. The non-elec- 
trics on the contrary allow the free passage of electri- 
city from themselves to other bodies, they are therefore 
denominated conductors. Electricity does not remain 
upon a pith ball suspended by a wire, because it is im- 
mediately conducted away by the metal, unless some 
non-conductor intervene ; when silk is used to suspend 
a ball, the fluid is prevented from passing away, because 
this substance is a non-conductor. 

We can not here go into an explanation of the dif- 
ferent kinds and forms of apparatus calculated to illus- 
trate the phenomena of electricity, but must confine 
ourselves to those principles, a knowledge of which is 
necessary, to an understanding of the agency of elec- 
tricity in producing the organization of plants. 

That electricity exerts an important influence upon 
vegetation, can not be doubled, but the manner of its 
action is difficult of solution. We have before alluded 
to the fact that the ascent of sap in the living plant, is in 
part, owing to electricity. The following experiment 

What name is given to the electricity derived from glass? From 
rosin 1 What is said of bodies in different electrical states 1 In like 
electrical states? What are electrics? Non-electrics ? Conductors? 
Non-conductors? Does electricity exert any influence upon vegetation ? 
In what way ? 



ELECTRICITY. 133 

will tend to confirm this theory. Let a capillary tube 
bent in the form of a syphon be filled and connected 
with a vessel of water. The fluid will pass over slow- 
ly drop by drop: and while the water is being drain- 
ed out, connect it with the prime conductor of an 
electrical machine, or by some means charge it with 
electricity, and the fluid will commence running freely 
from the capillary tube. This serves to prove that the 
presence of electricity facilitates the passage of fluids 
through porous substances, and consequently may quick- 
en the circulation of sap in the plant, and make vegeta- 
bles more vigorous and healthy. It is in the power of 
the agriculturist to increase electrical action upon a lim- 
ited portion of the surface of the earth, but this princi- 
ple can not economically be applied except on a small 
scale, as in the rearing of house plants, or the cultiva- 
tion of garden vegetables. The mode of nourishing 
plants by electricity however depends upon a different 
modification of this force, and a short explanation of its 
peculiarities will be given. 

Galvanic Electricity is generally excited by the action 
of acidulated \vater upon metals of different kinds ; for 
instance, if a small plate of copper and a similar one of 
zinc, be immersed in very dilute acid, electricity will be 
generated, and the positive fluid will flow from the metal 
most easily oxidized to the other ; this will occur how- 
ever, only when the ends of the plates not immersed 
are connected, in that case the flow of electricity, is as 
stated before, from the zinc to the copper in the fluid, 
but from the copper to the zinc again out of the fluid, 
thus restoring the equilibrium. 

If the zmc be pure, there will be no unusual action, 
except when the two plates are connected. As soon 
as a communication is established between them, bub- 
Give the experiment with a capillary tube. What does this prove ? 
How is galvanic electricity excited 1 How must the plates be arranged 1 



3^4 AGEfClTLTUKAL CHEMISTRY. 

bles of hydro^^en begin to accumulate upon the coppers, 
and the zinc is rapidly oxidized ; the oxide is dissolved 
by the acid as it is formed, and electricity flows along 
the connecting substance. Non-conductors of electricity 
must not be used for connecting the plates ; but copper 
or brass wire, or some other ^ood conductor should be 
made the medium of communication. Two conducting 
wires, one connected with each plate, form the poles of 
the generating pair. 

If a fine wire of platinum be made the connecting 
substance, and the plates used are of sufficient size, the 
effect of the electricity will be to elevate the tempera- 
ture of the wire, until it becomes red hot : thus we see 
that electricity is a source of heat, and it is not only so 
with galvanic electricity, but the electricity drawn from 
a glass tube by friction may be made to fuse the differ- 
ent metals. 

Copper and zinc arranged as has been described, form 
what is called a Voltaic circle, and the electricity gen- 
erated arises from the decomposition of water, the hy- 
drogen of that compound passing to the copper, and the 
oxygen to the zinc. If several Voltaic pairs be united 
by connecting the zinc of one with the copper of the 
next and so on, having the poles connected with the 
extreme copper and zinc plates, the intensity of the cur- 
rent will be increased. To this form of apparatus the 
term battery is applied, although a single pair is some- 
times called by the same name. 

If the poles of a battery of four or five pairs are im- 
mersed in a vessel of water, the decomposition of that 
fluid is effected, and the hydrogen passes to the negative 
pole, or that connected with the zinc, and rises in minute 

What is the effect when the two plates are connected 1 What are the 
poles of a galvanic pair ] Give the effect of electricity upon platinum. 
From what does the electricity arise ? What becomes of the oxygen 
and hydrogen of the water? How may the intensity of the current be 
increased 1 What is the effect of a small battery upon water ? 



ELECTRICITY. 135 

bubbles to the surface ; the oxygen in a similar manner 
is disengaged at the positive pole ; the poles should be 
pointed with platinum or gold. 

These phenomena are explained by supposing that the 
elementary atoms of which water is composed, are in 
opposite states of electricity, and therefore, the hydro- 
gen being positive passes to the negative pole, but the 
oxygen being negative is attracted to the positive. Dif- 
ferent compounds are decomposed on the same principle. 
Potash subjected to the action of a powerful battery, 
yields its oxygen to the positive pole, and the metal po- 
tassium is collected at the other. Soda suffers a similar 
decomposition, and the metals sodium and potassium 
were first obtained by means of the galvanic battery. 
The metals pass to the negative pole, but oxygen, chlo- 
rine, sulphur, &c., are attracted by the positive. 

Many batteries, differing in form and power, have 
been constructed, the most simple and efficacious of 
which, is that invented by Professor Grove of London. 
The metals used are platinum and zinc ; the latter is 
coated with mercury, because the metal is impure, and 
by amalgamating it, the rapid solution of it in the acid 
which would otherwise take place, is prevented, and 
the galvanic action is more uniform and constant. A 
small thin slip of platinum is used and is acted upon by 
strong nitric acid, but as this acid would be too strong for 
the zinc, the two metals are arranged in different cups 
and acted upon by separate fluids ; the cup containing 
the platinum is of porous earthenware, and is placed 
within the other, which may be an ordinary glass tum- 
bler ; in the latter is placed a coil of amalgamated zinc 
which is acted upon by dilute sulphuric acid. The po- 
rous cup permits the free passage of electricity but does 

Give an explanation of the changes that occur. Give the effect of the 
battery upon potash, soda. How were potassium and sodium first ob- 
tained ] Describe Grove's battery. Why is a porous cup used 1 



k 



136 AGRICULTURAL CHEMISTRY. 

not allow the fluids to intermingle to any great extent. 

Here, as in the first form of the battery, the electric 
force arises from the decomposition of water; the oxy- 
gen passes to the zinc as before, but the hydrogen does 
not collect upon the platinum plate as it does upon the 
copper in the other battery, but passing into the nitric 
acid, decomposes it ; uniting with a part of its oxygen 
and causing an evolution of deutoxide of nitrogen. 

It has been before suggested that galvanic electricity 
has been applied to growing plants. A single pair of 
copper and zinc plates is generally applied. It is not 
necessary that any particular fluid should be employed 
for exciting galvanic action ; it is only important that it 
have the power of oxidizing the zinc Moisture will pro- 
duce the requisite effect and moist substances, forming 
a communication between the plates will excite a vol- 
taic current. If therefore a large plate of copper and 
a similar one of zinc be imbedded in moist earth, facing 
each other, and connected together by means of a cop- 
per w^ire which passes through the air and is soldered 
to each, an electric current will be generated which 
must pass through the intervening earth, and influence 
the growth of vegetable forms that occupy that space. 
It is in this way that electricity is applied to hasten the 
maturity of plants. The favorable action of electricity 
upon vegetation is perhaps in part owing to its decom- 
posing power ; indeed it is quite probable that the dif- 
ferent compounds taken up by the plant are decomposed 
by a kind of electric force residing in the plant, and thus 
the different elements are assimilated ; if so the reason 
is apparent why vegetation is assisted by the applica- 
tion of galvanic electricity. 

How are plants acted upon by galvanic electricity ? To what irmy 
the favorable action of electricity upon vegetation be owing ? 



LIGHT. 137 



LIGHT. 



Light was formerly supposed to be occasioned by the 
emanation of minute particles of matter from the sun, 
but this theory has been abandoned, and it is now gener- 
ally conceded that there exists a subtile elastic medium 
which is thrown into vibrations by the presence of the 
luminous body. 

Light is a powerful chemical agent and although silent 
in its operations is continually promoting chemical chan- 
ges. It is essential to the perfection of vegetable forms, 
and is supposed to be necessary to the health of the 
animal frame. It is sometimes said to be composed of 
seven colors, violet, indigo, blue, green, yellow, orange^ 
and red, because by means of ^ prism we can produce 
these several colors from a single ray of white light ; 
yet strictly speaking this elastic medium of which we 
have spoken can not be said to be composed of different 
colors. The waves of light produced by the vibration 
of the medium have been found to be of different lengths, 
according to the colors displayed, and thus different 
shades of color are produced in much the same way 
that different musical sounds are caused by difference 
of vibration in the medium of communication. 

In the vegetable world the various changes necessary 
to produce a healthy plant can not occur without the pres- 
ence of light. During the day carbonic acid gas is ab- 
sorbed by every green leaf, but during the night this 
process, which is so necessary to the perfection of the 
plant, does not continue. Plants will grow to some 
extent in the shade or even in a dark cellar, but they are 
pale and sickly ; the bright green color can not be pro- 

What was formerly supposed with regard to light, and what is now 
conceded 1 What is said of it as a chemical agent 1 How many colors 
are exhibited by the decomposition of light ? To what are they owing ? 
What process goes on during the day in the leaves of plants ? How is 
it during the night ? 

*2 



^ 



138 AGRICULTURAL CHEMISTRY. 

duced but by the influence of light. The leaves of sonne 
plants follow the sun in its course, and it is a well known 
fact that growing vegetables stretch their foliage in the 
direction whence m'ost light is received. It will be no- 
ticed that the trees lining roads which pass through the 
forest, have the greater share of their foliage stretching 
towards the opening caused by the road. 

The nneansby which the plant is supplied with carbon 
have been pointed out; but carbonic acid after it has been 
absorbed by the leaves, must be decomposed by light, 
otherwise no carbon will be assimilated. The changes 
that occur by day in vegetable forms may be illustrated, 
by placing sonae green leaves in a vessel of spring water, 
and placing it inverted in a second vessel containing 
water. (See Fig. 20.) 

Fig. 20. If the leaves be exposed to the action of sun- 
light, small bubbles of gas will rise from them 
'and collect in the upper part of the vessel. By 
examination it will appear that the carbonic acid 
which was dissolved in the water has been taken 
up by the leaves, decomposed by the action of 
light, and oxygen given off. 

The agency of light in producing the organization of 
plants has been distinctly shown by the researches of 
Dr. Draper. The following extracts will illustrate his 
views. 

" Organized beings, and organized bodies spring forth 
in those positions only to which the rays of the sun have 
access. They are, therefore limited to the atmosphere, 
the sea, and the surface of the earth. Periodical vicis- 
situdes, which are observed both in vegetables and in 
animals, serve to show that this is not a mere fortuitous 
coincidence, but rather an intimate connection between 

State facts showing the influence of light upon plants, trees, <Slc. 
State the experiment given. 




LIGHT. 139 

the phenomena of life, and the presence of the impon- 
derables. When the sun is set, the leaves of plants 
no longer decompose the carbonic acid of the air, but 
a pause takes place in the activity of their functions, 
and they sink into a passive condition. The gaseous 
bodies brought from the ground by the action of the 
spongioles percolate through the delicate tissues of the 
leaf, and escape away into the atmosphere. At night, 
also, in many flowers, the petals fold themselves togeth- 
er, and, for a time, all active processes cease." 

" The general principles of life carried on in the 
water are modelled on the same idea as in the case of 
life carried on in the air. In both cases, vegetables act 
as the great formative agents, and animals as the de- 
structive power ; and in both, the source and origin of 
action is to be found in the beams of the sun. For 
nearly two centuries, physical science has fully admit- 
ted the agency of that central star, as the great seat of 
mechanical force, which retains the different planets in 
their orbits. It is only of late years that we are begin- 
ning to recognize his agency as the author of organiza- 
tion and life, who lays up, with an almost provident 
foresight, in vegetable productions, stores of light and 
heat for the use of the animal world. The coal fields 
which furnish us with fuel are the remains of primeval 
forests, among the branches of which, birds nestled at 
night ; and the warmth that we receive from them, and 
the light that they give us, have been safely stored up 
for us for thousands of centuries. Those little insects, 
also, which at certain seasons cause the sea to shine 
with a phosphorescent light, derive their glow remotely 
from the vegetable kingdom : and the fire flies which, in 
such countless multitudes, on a summer evening in Vir- 
ginia, make the grass and trees glitter with their inter- 

What does Draper say of the leaves of plants after sunset 1 What of 
the great influence of the sun 1 Of phosphorescent iasects ? 



140 AGRICULTURAL CHEMISTRY. 

mitting beams, are only pouring forth again rays which 
once came from the sun." 

" If a few garden seeds of any kind are sown in a 
flowerpot, and caused to germinate in a dark room, after 
a while it will be perceived that they can grow for a 
certain space in the absence of light ; their young 
leaves, if any should be put forth, are of a yellow or 
gray-white color, and tliey soon fade away and die. 
But if these plants be brought out into the light, they 
presently begin to turn green, they unfold their leaves, 
and evolve their different parts in a natural way. From 
day to day their weight increases, and chemical analy- 
sis shows that they are fixing carbon, hydrogen, oxygen, 
and azote, (nitrogen.) If they be made to grow in confin- 
ed glass vessels, under such circumstances that an exami- 
nation can be instituted on the changes they are impres- 
sing on the atmosphere, it is discovered that they are 
constantly abstracting carbonic acid from it, and as long 
as the sun shines on them, or as long as they are exposed 
to bright daylight, they continue appropriating carbon 
and exhaling a mixture of oxygen and nitrogen. The 
continuance of their growth depends on a continued 
supply of the acid gas in due quantities. The leading 
facts which are here mentioned were discovered during 
the last century by Priestly, who found that when 
leaves of any kind are placed in water, which holds 
carbonic acid gas in solution, they evolve oxygen when 
in the sunshine. It is not pure oxygen, but a mixture of 
that gas with azote." 

The last remark seems to be introduced, because it 
is generally stated that pure oxygen is given off by the 
growing plant, while not only this but nitrogen and even 
carbonic acid are thrown oflf in minute quantities during 

What is said of plants growing in the dark ? What changes are 
impressed upon the air by plants exposed to sunlight 1 What is gener- 
ally said to be given off by the plant? 



I 



LIGHT. HI 

the decompositions that take place in the tissues of the 
plant. The water of the vegetable structure has the 
power of absorbing all these gases, but in different 
quantities ; nitrogen is slowly absorbed, oxygen more 
rapidly, and carbonic acid with still greater facility, and 
in the decomposition produced by sunlight, all are re- 
leased, but principally oxygen ; the last mentioned gas, 
however, may not be derived wholly from the carbonic 
acid, for there are strong indications that light not only 
decomposes this acid but water itself, and since, as we 
have before stated, there is an excess of hydrogen in 
most plants, a portion of oxygen derived from water 
probably escapes. The author from whom we have^ 
just quoted, has endeavored to determine the kind of 
light which is most active in producing the requisite 
decompositions. By investigating the subject he has 
determined that of the four distinct principles of which 
light is made up, viz. calorific^ tithonic or chemical, 
phosphorescent and luminous rays, the latter are princi- 
pally concerned in the decomposition of water, and car- 
bonic acid in the plant. The following are some of his ar- 
guments and experiments tending to prove his position. 
"First let us ascertain whether radiant heat, general- 
ly, has the quality of producing decomposition. To 
rays coming from a brightly-burning fire, I exposed 
some vegetable leaves in water holding carbonic acid 
in solution, and, to increase the effect converged the 
calorific rays by a large metallic concave mirror. That 
no doubt might remain of the incapacity of heat to pro- 
duce the phenomenon, the temperature of the water, 
under the influence of the radiant heat was allowed to 
run up to 140^^ Fah., a much higher point than is ever 
attained under natural circumstances. But neither at 
low temperatures, nor at these elevated ones, did any 

Are other gases evolved ? Name them. Is the oxygen thus evolved 
derived wholly from carbonic acid 1 From what else ? 



k 



142 AGRICULTURAL CHEMISTRY. 

visible decomposition take place ; showing thus, that 
heat alone can not cause the digestion of plants. More- 
over, as is well known to chemists, carbonic acid gas 
may be passed through a tube that is white hot, with- 
out giving the most remote appearances of decompo- 
sition." 

Other experiments seemed to indicate, that the heat 
of the different colored rays, did not produce the 
required effect. 

" That the decomposition of carbonic acid by leaves is 
not due to yellow heat, may be proved by causing the 
active light to pass through a solution of bichromate of 
potash, which is of an orange-yellow color. This ray, 
thus treated, appears to carry on the decomposition with 
nearly the same activity as the direct solar beams. In 
an experiment which 1 made, using it in a stratum of 
certain thickness, it seemed to transmit the yellow and 
orange light with very little loss ; but acting more en- 
ergetically on the calorific ray, it transmitted of it only 
•26. Had this heat been the cause of the decomposition, 
the rapidity with which the action took place should 
have been proportionally reduced. 

From such results, it is to be inferred that radiant 
heat generally, and the yellow rays of heat especially, 
do not produce the decomposition of carbonic acid gas 
in the structure of vegetable leaves. 

This narrows the question down to the inquiry, whether 
it be the yellow ray of light, or the yellow tithonic ray ; 
for, as has been observed, the phosphorescent rays may 
be left out of the discussion." 

That which is called the tithonic ray, by this author 
has heretofore been denominated the chemical ray, on 

By what experiment is it shown that radiant heat does not produce 
the decomposition that takes place in the tissues of the plant 1 State the 
experiment with the heat of the yellow ray. What is the tithonic ray 
referred to ? 



LIGHT. 143 

account of its agency in producing chemical combina- 
tions. It is this ray which destroys colors in the process 
of bleaching, and the same principle occasions the ex- 
plosive combination of hydrogen and chlorine in the 
experiment given on page 51. It is a curious fact that 
the luminous power of light may be wholly destroyed 
by passing it through certain substances, while its chem- 
ical power is unchanged. 

It is well known that the diamond after being exposed 
to the sun, will be seen to give out light when carried 
into a dark place. To the rays thus absorbed and af- 
terwards given out, the term phosphorescent is applied. 

The experiments of Draper last referred to, were 
made with the yellow rays ; they had been proved be- 
fore to be most active in aiding vegetable organization, 
but it was still a question, whether the result was pro- 
duced by the calorific, chemical, or luminious ray of the 
yellow light. A solution of the bichromate of potash 
was found to diminish the force of the chemical ray 
when light was passed through it, so much so, that the 
rays thus treated effected very slowly those substances 
that are under ordinary circumstances rapidly decom- 
posed by the chemical ray. Yet the yellow fight pro- 
duced by such a solution, caused a rapid decomposition 
of carbonic acid when the plant was under the influ- 
ence of it. From all the results obtained by experi- 
ment, the inference is that "^o the light, and more 
especially to the yellow light of the sun, we are to impute 
the most interesting phenomena of organic chemistry. ^^ 

In this connection it may be well to reconsider the 
phenomena connected with capillary attraction since 
light controls the movement of the sap to a great extent, 
and determines the rapidity of the circulation. 

State the chemical effects of this ray. What are phosphorescent rays t 
What was the effect of a solution of bichromate of potash upon the 
chemical ray of yellow light 1 



144 AGRICtTLTURAL CHEMISTRY. ^ 

It is well known that a porous substance will be more 
easily penetrated by some fluids than by others. Weak 
alcohol may be concentrated by putting it into a blad- 
der, and permitting the water to pass through the pores, 
the alcohol will be retained, because it does not easily 
pass through the porous membrane. If a bladder filled 
with alcohol and tied perfectly tight, be placed in a ves- 
sel of water, the two liquids will intermingle, the water 
in the vessel will be found by examination to contain 
alcohol, and the water without will slowly pass into the 
bladder ; these effects are due to the action of the capil- 
lary force, for if two different fluids be permitted to 
communicate through a capillary tube, or a porous 
membrane which is made up of an infinite number of 
such tubes, a current will be established in each direc- 
tion, and there will be a gradual intermingling of the 
two. If one of the fluids employed has a tendency to 
pass through the porous substance more rapidly than 
the other, the result will be an accumulation of fluid, on 
one side of the capillary division, and a diminution on 
the other. As a result of the action of this principle, 
the bladder in the experiment just given, is distended 
and finally bursts, because the water passes in with 
greater rapidity than the alcohol passes out. A similar 
illustration is given in the remarks on capillary attrac- 
tion. 

The passage of gases through a membrane illustrates 
the same principle ; if a piece of India rubber be tied 
over the mouth of a jar, so tightly, that there can be no 
communication except through the pores of the cover- 
ing, and the vessel be placed under a bell-glass filled 
with ammonia, the ammoniacal atmosphere will pass 
into the vessel so rapidly, as to distend considerably the 

How may water be separated from weak alcohol 1 Describe the ef- 
fect of immersing a bladder of alcohol in water. Why is there an accu- 
mulation within the bladder X What experiment illustrates the similar 
passage of gases through a porous membrane ] 



LIGHT. 145 

elastic coveiing. Draper has discovered that" sulphur- 
oud acid will pass into atmospheric air against a press- 
ure of one hundred and ten pounds on the square inch, 
and sulphuretted hydrogen wiil move through a mem- 
brane with a force that is superior to a pressure of 
twenty-four atmospheres." 

By appplying the principle thus elicited by experi- 
ment, the true cause of the circulation of the sap in the 
plant in both directions is made evident. The sunlight 
by its decomposing action upon the carbonic acid dis- 
solved in the sap of the leaf, changes the nature of that 
liquid, charging it with carbon and perhaps an excess of 
hydrogen ;thus the plant is supplied with two fluids, and 
all the conditions are fulfilled that occasion the passage 
of liquids in different directions through capillary tubes. 
Light then by its action, produces the condition neces- 
sary to the exertion of the capillary force. 

Allusion has been made to the similarity of action in 
many respects of the different chemical forces, and it 
seems not improbable that capillary attraction is only a 
modification of electrical attraction. The tendency of 
all late researches with regard to the different chem- 
ical forces, has been to show new similarities and to 
bring them nearer and nearer together. 

What is said of sulphurous acid and sulphuretted hydrogen 1 What 
effect does light produce upon the sap of the plant ? Capillary attraction 
may be a modification of what ? 



PART V. 

FERTILIZERS 



MINERAL, ANIMAL, AND VEGETABLE MANURES, 

Preliminary Observations. 

Seed time and harvest are promised to the tillers of 
the soil, but this is not an unconditional promise. Man 
may not fold his arms, and in sleep await the growing 
grain and ripening harvest, and still expect the blessing. 
Experience has taught him that unless nature's requisi- 
tions be complied with, unless ihe earth be fitted to re- 
ceive the seed and the germ of future plants be proper- 
ly consigned to it, no harvest will ensue. The various 
forms of the vegetable world-like animal existence, re- 
quire food, drink, and an atmosphere fitted to their 
wants ; these are amply supplied where nature is her owd 
husbandman, for she faithfully returr>s to the earth what 
she has withdrawn from it, even returns much more 
than she has received. The mighty oak gathers its 
strength from the earth and air, but after having with- 
stood the shock of many a tempest and passed through 
the various changes of springtime freshness, and 
autumnal blight ; it falls and mingles with the dust from 
which it sprang ; thus returning, with interest, the atoms 
gathered from the earth. 

The forest trees, made up in part of the inorganic 
matter of the soil, when they sink to earth, bear with 
them a mass of atoms that once floated in the atmos- 
phere. Thus it is that, unassisted by art, the soil upon 
which the forests stand does not become impoverished,. 



FERTILIZERS, 147 

but on the contrary increases in fertility each succeed- 
ing year. The dark rich mould accumulatiug upon the 
surface is mostly gathered from the air and this gives 
new vigor to each successive growth. But not so in 
the fields whence man continually draws the necessaries 
of life and the sources of wealth and enjoyment. The 
earth yields of its substance to each growing plant that 
is cultivated by man, and every crop removed, in a 
measure weakens and exhausts the soil. Thus it follows 
that, however rich a soil may be, continued cropping, 
without a corresponding return in some available form, 
will produce barrenness. 

The plant just as imperatively demands food, and 
that of a kind adapted to its nature, as does the animal 
system, yet if we may judge from the practice of many 
of the tillers of the soil, there is not that knowledge or ap- 
preciation of the wants of vegetable life, which the 
importance of the subject demand. It seems to be often 
forgotten by agriculturalists that vegetable forms, 
can not be produced in the great laboratory of nature un- 
less there be a supply of the raw materials. Too much 
faith is manifested in the ability of nature to create from 
nothing \\\o^Q forms so necessary to the existence of all 
living beings. The materials of which plants are formed 
and the sources from which they may be derived have 
been pointed out. A general examination of the effica- 
cy of the different fertilizers, that can be economically 
applied by the agriculturalist, will now be given. 



148 AGRICULTURAL CHEMISTRY. 

SECTION I. 

MINERAL MANURES. 
Lime, 

If we examine the nshes of plants, a portion, and in 
some cases a large portion of lime will be found. It is 
therefore evident that a certain proportion of this sub- 
stance is essential to perfect vegetable organization, and 
should be contained in the soil. Most soils contain some 
lime, because they are formed by the disintegration, 
or wearing down, of the different rocks, and many of 
these contain this mineral ; in many localities it occurs 
in mountain masses nearly pure and in inexhauslabie 
quantities. 

The term lime, in a chemical sense, applies only to 
the burned lime before it has been slacked ; after being 
slacked it is a hydrate of lime; by exposure to the 
air this become gradually changed to a carho7iate and 
in this condition has the same chemical constitution as 
when taken from the quarry ; the term lime however, 
will be indiscriminately applied to the various forms 
mentioned, the term quicklime being used to designate 
the unslacked whenever it is necessary to do so. 

The importance of this mineral as a manure, by no 
means depends wholly upon the demand of the plant 
for lime as food ; in numerous ways it facilitates the 
process of vegetation, and aids in the production of veg- 
etable forms. 

1. A certain amount differing in different plants is 
all essential to the perfection of the vegetable structure. 

2. The action of lime upon the vegetable matter in 
the soil renders it fit to supply nourishment to the plant. 

Does lime occur in the ashes of plants ? What effect is produced upon 
Ime by slacking? By exposure to the air ? In what different ways does 
lime promote vegetation ? 



MINERAL MANURES. 149 

3. Lime seems to neutralize noxious compounds, 
destroys useless weeds and coarse grasses; and expels 
worms and insects that infest the soil. 

4. The stifF, clayey soils are, by the application of lime, 
rendered loose and porous, less retentive of moisture 
and therefore warmer, and made to release ammonia 
which is often held with great tenacity by such soils. 

Lime as a source of nourishment, probably exerts a 
less important influence, than as an agent through which 
the soil and vegetable manures are fitted to promote 
vegetation. Yet nrdny plants require no inconsiderable 
share of food in the form of lime, as will be indicated by 
ihe following table given by Johnston. The average 
produce of an acre of land, under the following crops, 
<iontains of lime — 





Grain, or roote 


Straw, .or 


tops. Total. 


Wheat, 25 bushels. 


1-5 


7-2 


8-7 lbs 


Barley, 38 " 


2-1 


12-9 


15 " 


Oats, 50 " 


2-5 


.5-7 


8-2 " 


Turnips, 25 tons. 


45-8 


93-0 


138-8 " 


Potatoes, 9 " 


6-6 


259-4 


266-0 " 


Red clover, 2 " 
Rye grass, 2 " 




126- 
33- 


126- " 
33- " 







On account of the amount of lime m the ashes of 
certain plants, they are called lime plants, but it is a 
curious and somewhat important property of some of 
these, that potash may be made to take the place of 
iime. This is the case to a certain extent, with the 
tobacco plant, which is generally ranked among lime 
plants, but has been so cultivated as to assimilate more 
potash than lime, thus producing a more valuable arti- 
cle of tobacco. 

Show something of the different quantities of lime withdrawn from an 
acre of land by different crops? What are those plants called that con- 
tain a large quantity of lime ? What may take the place of lime ? 



150 AGRICULTURAL CHEMISTRY. 

Action of Lime upon Vegetable matter. 

The mode in which caustic lime produces the requi- 
site changes in vegetable matter contained in the soil, is 
thus stated by the author last quoted. 

'' In the presence of" air and water, when assisted by 
a favoring temperature, vegetable matter, as we have 
already seen, undergoes spontaneous decomposition. In 
the same circumstances lime promotes and sensibly 
hastens this decomposition ; altering the forms or sta- 
ges through which the organic matter must pass ; but 
bringing about more speedily the final conversion into 
carbonic acid and water. During its natural decay in 
a moist and open soil, organic matter gives off a por- 
tion of carbonic acid gas, which escapes and forms 
certain other acids which remain in the dark mold of 
the soil itself. When quick or slacked lime is added to 
the land, its first effect is to combine with these acids — 
to form carbonate, humate, &c , of lime — till the whole 
of the acid matter existing at the time is taken up. That 
portion of the lime which remains uncombined, either 
slowly absorbs carbonic acid from the air or unites with 
the carbonate already formed, to produce the known 
compound of hydrate with carbonate of lime, — waiting 
in this state in the soil till some fresh portions of acid 
matter are formed with which it may combine. But it 
does not inactively wait ; it persuades and influences 
the organic matter to combine with the oxygen of the 
air and water with which it is surrounded, for the pro- 
duction of such acid substances — till finally the whole 
of the lime becomes combined either with carbonic or 
with some other acid of organic origin." 

*' Of the saline compounds which caustic lime thus 
forms either immediately or ultimately, some, like the 

State the effect of lime upon decomposing vegetable matter. What 
does it first combine with ? What is said of the insolubility of the dif- 
ferent compounds formed ? 



MINERAL MANURES. 151 

carbonate and humate, being very sparingly soluble in 
water, remain more or less permanently in the soil ; 
others, like the acetate of lime, being readily soluble, 
are either washed out by the rains or are sucked up by 
the roots of the growing plants. In the former case 
they cause the removal of both organic matter and of 
lime from the land ; in the latter they supply the plant 
with a portion of organic food, and at the same time 
with lime — without which, as we have frequently before 
remarked, plants cannot be maintained in their most 
healthy condition." 

" The main utility of lime depends upon its prolonged 
after action upon the vegetable matter of the soil. 
What is this action, and in what consist the benefits to 
which it gives rise ? 

In answering this question, it is of importance to ob- 
serve that all the effects produced by alkaline matter in 
general — whether by lime or by potash— in the caustic 
state, are produced in ki7id aho by the same substances 
in the state of carbonate. The carbonic acid with which 
they are united is retained by a comparatively feeble 
affinity, and is displaced with greater or less ease by 
almost every other acid compound which is produced 
in the soil. With this displacement is connected an in- 
teresting series of beautiful reactions, which it is of con- 
sequence to understand. 

You will recollect that the great end which nature, 
so to speak, has in view, in all the changes to which she 
subjects organic matter in the soil, is to convert it — with 
the exception of its nitrogen — into carbonic acid and 
water. For this purpose it combines, at one time, with 
the oxygen of the air, while at another it decomposes 
water and unites with the oxygen or the hydrogen 
which are liberated or with both to form new chemical 

Is the same effect produced by the carbonate as by the caustic lime ? 
Into what is organic matter mostly converted ? 



152 AGRICULTURAL CHEMISTRY. 

combinations. Each of these new combinations is 
either immediately prehminary to oris attended by the 
conversion of a portion of the elements of the organic 
matter into one or other of those simpler forms of 
matter on which plants live. Now during these prelimi- 
nary or preparatoay steps, acid substances, as I have 
already explained, are among others constantly pro- 
duced. With these acids, the carbonate of lime, when 
present in the soil, is ever ready to combine. Butin so 
combining it gives off the carbonic acid with which it 
is already united, and thus a continual, slow evolution 
of carbonic acid is kept up as long as any undecom- 
posed carbonate remains in the soil. 

The changes, therefore, which lime and organic mat- 
ter, supposed to be free from nitrogen, respectively un- 
dergo, and their mutual action in the soil, may be sum- 
med up as follows: — 

1. The organic matter, under the influence of air 
and moisture, spontaneously decomposes, and besides 
carbonic acid which escapes, forms also other acid sub- 
stances which linger in the soil. 

2. With these acids the quick-lime combines, and, 
either by its union with them or with carbonic acid 
from the air, soon (comparatively) loses its caustic state. 

3. The production of acid substances by the oxida- 
tion of the organic matter— goes on more rapidly under 
the disposing influence of the lime, whether caustic or 
carbonate. These acids combined with the lime, liber- 
ating from it, when in the state of carbonate a slow but 
constant current of carbonic acid, upon which plants at 
least partly live. 

4. The organic acid matter which thus unites with 
the lime continues itself to be acted upon by the air and 

What is the effect of the acids in the soil upon the carbonate of lime ? 
What is given off] State the different changes produced by lime and 
organic matter? 



MINERAL MANURES. 153 

water, aided by heat and light, itself passes through a 
succession of stages of decomposition, at each of which 
it gives off water or carbonic acid, retaining still its 
hold of the lime, till at last being wholly decomposed it 
leaves the lime again in the state of carbonate, ready to 
begin anew the same round of change." 

Lime then acts an important part in the preparation 
of food for the plant, and is ever producing changes in 
the soil, if vegetable matter be present, that are produc- 
tive of good results. Upon light sandy soils, the appli- 
cation of lime unaccompanied by vegetable manures, 
would be worse than useless ; its mechanical effect 
would be to make more loose and porous a soil already 
too permeable, or, by combination with the sand, to form 
hard, lumpy masses unfavorable to vegetation and re- 
sisting the different pulverizing agencies, both natural 
and mechanical. A proper admixture of lime however, 
either caustic or in the form of a carbonate, with the 
different forms of vegetable manure, will enrich most 
soils, giving them a productiveness of which they seemed 
before incapable. 

The action of lime is not limited to the production of 
the changes just described ; it is instrumental also in 
producing ammonia for the plant, as has been before 
intimated. The following experiment somewhat similar 
to one given in another place, will indicate its action in 
this respect. Quicklime and clay intermixed and 
moistened, will evolve ammonia ; this gas seems to be 
confined by the clay, but the action of lime releases it. 
Ammonia is also evolved by the decomposition by means 
of lime of those vegetable substances that contain 
nitrogen ; upon this point Johnston uses the following 
language. 

Give the effect of lime upon sandy soils when unaccompanied by vege- 
table matter. What other effect does lime produce? How may ammo- 
nia be released from its combination with clay. 



154 AGRICULTURAL CHEMISTRY. 

" I have hitherto, for the sake of simplicity, directed 
your attention solely to the action, whether immediate 
or remote, which is exercised by lime upon organic 
matter supposed to contain no nitrogen. Its action 
upon compounds in which nitrogen exists is no less 
beautiful and simple, perhaps even more intelligible and 
more obviously useful to vegetation. 

There are several well known facts which it is here 
of importance to consider : — 

1. That the black vegetable matter of the soil 
always contains nitrogen. Even that which is most 
inert retains a sensible proportion of it. It exists in dry 
peat to the amount of about 2 per cent, of its weight, 
and still clings to the other elements of the organic 
matter, even after it has undergone those prolonged 
changes by which it is finally converted into coal. 
Since nitrogen, therefore, is so important an element in 
all vegetable food, and so necessary in some form or 
other to the healthy growth and maturity of plants, it 
must be of consequence to awaken this element of de- 
caying vegetable matter, when it is lying dormant, and 
to cause it to assume a form in which it can enter into 
and become useful to our cultivated plants. 

2. That if vegetable matter of any kind be heated 
with slacked lime, the whole of the nitrogen it may 
contain, in whatever state of combination it may pre- 
viously exist, will be given off in the form of ammonia. 
The same takes place still more easily if a quantity of 
hydrate of potash or of hydrate of soda be mixed with 
the hydrate of lime. Though it has not as yet been 
proved by direct experiment — yet I consider it to be 
exceedingly probable, that what takes place quickly in 
our laboratories, at a comparatively high temperature, 

What does the black vegetable matter of the soil always contain ? 
What effect is produced by heating vegetable matter with slacked lime ? 



MINERAL MANURES. 155 

may take place more slowly also in the soils, and at the 
ordinary temperature of the atmosphere. 

3. That when animal and vegetable substances are 
mixed with earth, lime, and other alkaline matters, in 
the so-called nitre beds, ammonia and nitric acid are 
both produced, a quantity of nitrogen contained in the 
weight of these compounds extracted being much great- 
er than was originally present in the animal and vegeta- 
ble matter employed. Under the influence of alkaline 
substances, therefore, even when not in a caustic state, 
the decay of animal and vegetable matter in the pres- 
ence of air and moisture causes some of the nitrogen of 
the atmosphere to become fixed in the soil in the form 
of ammonia or nitric acid. What takes place on the 
confined area of a nitre-bed, may take place to some 
extent also in the wider area of a well-limed and well- 
manured field." 

" In the action of alkalies in the nitre-bed, disposing 
to the production of nitric acid, we observe the same 
kind of agency, which we have already attributed to 
lime, in regard to the more abundant elements which 
exist in the vegetable matter of the soil. It greatly 
persuades all the elements — nitrogen and carbon alike — 
to unite with the oxygen of air and water, and thus ul- 
timately to form acid compounds with which it may 
itself combine." 

" The action of lime upon such organic matters con- 
taining nitrogen as usually exist in the soil, may there- 
fore, be briefly stated as follows : — These substances, 
like all other organic matters, undergo in moist air — and 
therefore, in the soil' — a spontaneous decomposition, the 
general result of which is the production of ammonia, 
and of an acid substance with which the ammonia may 
combine." 

What effect is produced in nitre beds 1 Where is a similar effect pro- 
duced % What is produced besides ammonia by the action of lime upon 
organic matter 1 



156 AGRICUI^TURAL CHEMISTRY. 

" If the ammonia happens to be produced In larger 
relative quantity than the acids with which it is to com- 
bine, or if the carbonic acid be the only acid with which 
it unites a portion of it may escape into the air. This 
rarely happens, however, in the soil, the absorbent prop- 
erties of the earthy matters of which it consists,- being 
in most cases sufficient to retain the ammonia, till it can 
be made available to the purposes of vegetable life. 

When caustic (hydrate of) lime is added to a soil in 
which ammonia exists in this state of combination with 
acid matter, it seizes upon the acid and sets the ammo- 
nia free. This it does with comparative slowness, how- 
ever, for it does not at once come in contact with it all 
— and by degrees, so as to store it up in the pores of the 
soil till the roots of plants can reach it, or till it can 
itself undergo a further change by which its nitrogen 
may be rendered more fixed." 

*' Carbonate of lime, on the other hand, still more 
slowly persuades the ammonia to leave the acid sub- 
stance (ulmic, nitric, &c.,) with which it is combined, 
and yielding to it in return its own carbonic acid, ena- 
bles it in the state of soluble carbonate of ammonia to 
become more immediately useful to vegetation." 

The effect of lime upon noxious compounds. 

It has been stated that the sulphate of iron is some- 
times formed in the soil and injuriously effects vegeta- 
tion. By the action of lime this salt is decomposed and 
the resulting compounds possess fertilizing qualities ; sul- 
phate of lime (gypsum) and oxide of iron are formed ; 
the former is a well known fertilizer and the latter, by 
absorbing oxygen from the air becomes servicable to 
the plant. 

With what do these acids combine 1 State the effect of caustic lime 
upon ammonia already combined with acids. What is said of carbonate 
of ammonia] How may the injurious effects of the sulphate of iron be 
prevented 1 



MINERAL MANURES. 157 

Lime exerts its decomposing action upon several oth- 
er compounds, some of which are pointed out in the 
followino^ remarks. "Lime decomposes also the sul- 
phates of magnesia and alumina, both of which are 
occasionally found in the soil, and being very soluble 
salts, are liable to be taken up by the roots in such 
quantity as to be hurtful to the growing plants. When 
soils which contain the salts I have mentioned, have 
once been limed or marled, it is in vain to add gypsum 
in the hope of favoring the clover crop, since the lime, 
in decomposing the sulphates, has already formed an 
abundant supply of this compound for all the purposes 
of vegetation. 

Potash and soda exist to some extent in clay soils in 
combination with their alumina. The presence of lime 
has a similar influence in setting the alkalies free from 
this state of combination also." 

" In the presence of decaying organic substances, 
the carbonate of lime is capable of slowly decompo- 
sing common salt, producing carbonate of soda, and 
chloride of calcium. It exercises also a similar decom- 
posing efTect, even upon the sulphate of soda, and ac- 
cording to Berthollet, incrustations of carbonate of soda 
are observed on the surface of the soil, wherever car- 
bonate of lime and common salt are in contact with 
each other. If we consider that along all our coasts 
common salt may be said to abound in the soil, being 
yearly sprinkled over it by the salt sea winds ; that 
I generally, along the same coasts, the application of sul- 
1 phates produces little sensible effect upon the crops, and 
t that, therefore, in all probability they abound in the soil, 
(derived, it may be, from the same sea spray, we may 
ssafely conclude, I think, that the decomposition now ex- 

What other compounds does lime decompose ? In what cases is it 
ivain to apply gypsum ? What is the effect of carbonate of lime upon the 
lalkalies potash and soda? State its effect upon common salt. 



158 AGRICULTURAL CHEMISTRY. 

plained must take place extensively in all those parts of 
our island which are so situated, if lime in any of its 
forms either exists naturally or has been artificially ad- 
ded to the land. The same must be the case also in 
those districts where salt springs occur, and generally 
over the new red sandstone formation in which sea salt 
more especially occurs. 

And if we further consider the important purposes 
which the carbonate of soda thus produced may serve 
in reference to vegetation — that it may dissolve vegeta- 
ble matter and carry it into the roots — that it may form 
soluble silicates, and thus supply the necessary siliceous 
matter to the stems of the grasses and other plants, and 
that rising, as it naturally does, to the surface of the soil, 
it there, in the presence of vegetable matter, provokes 
to the formation of nitrates, so wholesome to vegetable 
life — we may regard the decomposing action of lime by 
which this carbonate is produced as among the most 
valuable of its properties to the practical farmer, wher- 
ever circumstances are favorable for its exercise." 

Like potash, lime seems to destroy coarse grasses and 
induce the growth of those more desirable. Its appli- 
cation upon soils infested by worms has sometimes re- 
sulted in the destruction of these destroyers of vegeta- 
ble life, although this is not a certain effect. 

Stiff, clay soils are greatly benefited by the applica- 
tion of lime, and the effect is of a twofold nature, me- 
chanical and chemical; such soils being generally too 
close and retentive of moisture, are rendered more 
permeable to water and air by the mechanical action 
of lime. The chemical action of this substance has been 
referred to, and the manner in which it releases ammo- 
nia pointed out. 

How do these changes produce a supply of silica for the plant ? What 
is the effect of lime upon noxious weeds, worms, &c. ? What are the 
two different effects of lime upon clay ] 



MINERAL MANURES. 159 

The question often arises among farmers, "In wiiat 
form shall we apply lime?" and some directions have 
already been given, but we will again state the differ- 
ence of the action of the various forms of lime. 

The rapid decomposition of anim.al or vegetable mat- 
ter is best effected by quicklime or the unslacked. But 
when the process of decomposition has been carried on 
to a considerable extent, the slaked lime or even that 
which has become a carbonate again will effect the re- 
quired changes. Caustic lime may be applied profita- 
bly to clover that is to be ploughed in as manure, and 
also to compost heaps that contain large quantities of 
undecomposed matter. 

No fertilizer is so generally beneficial, when applied 
to soils, as the one under consideration, and the facilities 
for obtaining it are such as to place it within the reach 
of most agriculturists. But some caution is necessary 
in the application of caustic lime, or it will produce un- 
favorable results. It must have something to act upon, 
and therefore decomposable matter should be contained 
in the soil, or should be applied in connection with the 
lime. New soils, which contain an abundance of vege- 
table matter, should receive a bountiful supply of lime ; 
indeed, in this way only can certain new soils be ren- 
dered fertile : and if the soil contains too much water, it 
always hinders, and sometimes prevents the required 
action of this fertilizer. 

It is sometimes asserted by agriculturists, that lime 
rapidly exhausts the soil. This is doubtless true, and 
the reason is apparent. Whenever a heavy crop is ob- 
tained from a piece of land, a large amount of matter is 
extracted from the earth, and therefore a great yield 

When should caustic lime be applied, and when the carbonate ? VVhat 
caution is given ] What is said of new soils ? If the soil contain too 
much water what will be the result ? What is asserted by agricultural- 
ists? Must not a good crop necessarily impoverish the soil to some 
extent. 



^ / / " 

160 AGRICULTURAL CHEMISTRY. 

necessarily exhausts the soil ; consequently, if lime, 
by rendering animal and vegetable matter soluble, and 
fitting it to become food for the plant, produces a large 
crop, it must be the indirect cause of exhaustion. This, 
however, can be no argument against the use of lime, 
since, without it, we should often be unable to avail 
ourselves of the matter in the soil. It is certainly advis- 
able to deprive a soil of its different fertilizing substan- 
ces by means of one good crop, rather than by two poor 
ones, and the immediate effect of cropping, in every 
case, is to exhaust the soil more or less. It is a neces- 
sary consequence then, that every large crop tends to 
wear out the land upon which it grows more rapidly 
than a light one can do, whatever fertilizers may be 
used. 

The action of lime in the compost heap, is more or 
jess important, according to the materials contained. — 
When common salt is one of the ingredients its decom- 
position is effected by the lime, the chlorine of the salt 
uniting with the calcium of the lime and forming the 
chloride of calcium, leaves soda in its caustic state, to 
act upon the vegetable and animal matter contained. — 
Soda quickly renders the decomposable matter soluble, 
and fits it for becoming food for the plant. Wood ashes 
contain the carbonate of potash in considerable quanti- 
ty, and when they form a part of the compost, lime de- 
composes this compound, and leaves the potash in its 
caustic state, and the process of decomposition is has- 
tened by the action of this alkali. 

VVould it be more economical to exhaust the soil by one heavy crop 
than by a series of light ones 1 What is the effect of lime upon common 
salt in the compost heap? What the effect upon carbonate of potash in 
wood ashes? What effect do caustic soda and potash produce ? 



LIBRARY OF CONGRESS 



DD0Eb71fll7A 




